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2016 (number)
2016 is the natural number following 2015 and preceding 2017. In mathematics * 2016 is a triangular number, being 1 + 2 + 3 + ... + 63. Equivalently, \tbinom = 2016. * 2016 is a 24-gonal number and a generalized 28-gonal (icosioctagonal) number . * 2016 has 36 divisors. * 211 − 25 = 2016. * 2016 forms a friendly pair with 360, as \dfrac = \dfrac = \dfrac = 3.25 and \dfrac = \dfrac = \dfrac = 3.25. The number 360 itself is a highly composite number, while 2016, while not highly composite, is highly composite among the positive integers not divisible by five. * 2016 × 2 + 1 = 4033. Although 4033 is not prime, as 4033 = 37 × 109, it is a strong pseudoprime to base 2 . Aside from 2016, the only other numbers below 10,000 with this property are 1023, 1638, 2340, 4160, and 7920. * There are 2016 five-cubes in a nine-cube. * 2016 is an Erdős–Nicolas number because, while not perfect, 2016 is the sum of its first 31 divisors (up to and including 288). * 2016 × 20 = 40,320 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Natural Number
In mathematics, the natural numbers are those numbers used for counting (as in "there are ''six'' coins on the table") and ordering (as in "this is the ''third'' largest city in the country"). Numbers used for counting are called ''Cardinal number, cardinal numbers'', and numbers used for ordering are called ''Ordinal number, ordinal numbers''. Natural numbers are sometimes used as labels, known as ''nominal numbers'', having none of the properties of numbers in a mathematical sense (e.g. sports Number (sports), jersey numbers). Some definitions, including the standard ISO/IEC 80000, ISO 80000-2, begin the natural numbers with , corresponding to the non-negative integers , whereas others start with , corresponding to the positive integers Texts that exclude zero from the natural numbers sometimes refer to the natural numbers together with zero as the whole numbers, while in other writings, that term is used instead for the integers (including negative integers). The natural ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
2015 (number)
2000 (two thousand) is a natural number following 1999 and preceding 2001. It is: :*the highest number expressible using only two unmodified characters in Roman numerals (MM) :*an Achilles number :*smallest four digit eban number Selected numbers in the range 2001–2999 2001 to 2099 * 2001 – sphenic number * 2002 – palindromic number * 2003 – Sophie Germain prime and the smallest prime number in the 2000s * 2004 – Area of the 24tcrystagon* 2005 – A vertically symmetric number * 2006 – number of subsets of with relatively prime elements * 2007 – 22007 + 20072 is prime * 2008 – number of 4 X 4 matrices with nonnegative integer entries and row and column sums equal to 3 * 2009 = 74 − 73 − 72 * 2010 – number of compositions of 12 into relatively prime parts * 2011 – Sexy prime with 2017, sum of eleven consecutive primes: 2011 = 157 + 163 + 167 + 173 + 179 + 181 + 191 + 193 + 197 + 199 + 211 * 2012 – The number 8 × 102012 − 1 is a prime number * 201 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
2017 (number)
2000 (two thousand) is a natural number following 1999 and preceding 2001. It is: :*the highest number expressible using only two unmodified characters in Roman numerals (MM) :*an Achilles number :*smallest four digit eban number Selected numbers in the range 2001–2999 2001 to 2099 * 2001 – sphenic number * 2002 – palindromic number * 2003 – Sophie Germain prime and the smallest prime number in the 2000s * 2004 – Area of the 24tcrystagon* 2005 – A vertically symmetric number * 2006 – number of subsets of with relatively prime elements * 2007 – 22007 + 20072 is prime * 2008 – number of 4 X 4 matrices with nonnegative integer entries and row and column sums equal to 3 * 2009 = 74 − 73 − 72 * 2010 – number of compositions of 12 into relatively prime parts * 2011 – Sexy prime with 2017, sum of eleven consecutive primes: 2011 = 157 + 163 + 167 + 173 + 179 + 181 + 191 + 193 + 197 + 199 + 211 * 2012 – The number 8 × 102012 − 1 is a prime number * 201 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Triangular Number
A triangular number or triangle number counts objects arranged in an equilateral triangle. Triangular numbers are a type of figurate number, other examples being square numbers and cube numbers. The th triangular number is the number of dots in the triangular arrangement with dots on each side, and is equal to the sum of the natural numbers from 1 to . The sequence of triangular numbers, starting with the 0th triangular number, is (This sequence is included in the On-Line Encyclopedia of Integer Sequences .) Formula The triangular numbers are given by the following explicit formulas: T_n= \sum_^n k = 1+2+3+ \dotsb +n = \frac = , where \textstyle is a binomial coefficient. It represents the number of distinct pairs that can be selected from objects, and it is read aloud as " plus one choose two". The first equation can be illustrated using a visual proof. For every triangular number T_n, imagine a "half-square" arrangement of objects corresponding to the triangular numb ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Friendly Number
In number theory, friendly numbers are two or more natural numbers with a common abundancy index, the ratio between the sum of divisors of a number and the number itself. Two numbers with the same "abundancy" form a friendly pair; ''n'' numbers with the same "abundancy" form a friendly ''n''-tuple. Being mutually friendly is an equivalence relation, and thus induces a partition of the positive naturals into clubs (equivalence classes) of mutually "friendly numbers". A number that is not part of any friendly pair is called solitary. The "abundancy" index of ''n'' is the rational number σ(''n'') / ''n'', in which σ denotes the sum of divisors function. A number ''n'' is a "friendly number" if there exists ''m'' ≠ ''n'' such that σ(''m'') / ''m'' = σ(''n'') / ''n''. "Abundancy" is not the same as abundance, which is defined as σ(''n'') − 2''n''. "Abundancy" may also be expressed as \sigma_(n) where \sigma_k denotes a divisor function with \sigma_(n) equal to the sum of t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
360 (number)
360 (three hundred sixty) is the natural number following 359 and preceding 361. In mathematics *The divisors of 360 are 1, 2, 3, 4, 5, 6, 8, 9, 10, 12, 15, 18, 20, 24, 30, 36, 40, 45, 60, 72, 90, 120, 180 and 360, making a total of 24 divisors. *360 is a highly composite number. Not only is 360 highly composite, but it is also one of only 7 numbers such that no number less than twice as much has more divisors; the others are 1, 2, 6, 12, 60, and 2520. . 360 is also a superior highly composite number, a colossally abundant number, a refactorable number and a 5-smooth number. *360 is the smallest number divisible by every natural number from 1 to 10 except 7. *One of 360's divisors is 72, which is the number of primes below it. *The sum of Euler's totient function φ(x) over the first thirty-four integers is 360. *A circle is divided into 360 degrees for the purpose of angular measurement. 360° = 2 π rad is also called a round angle. This choice of unit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Highly Composite Number
__FORCETOC__ A highly composite number is a positive integer with more divisors than any smaller positive integer has. The related concept of largely composite number refers to a positive integer which has at least as many divisors as any smaller positive integer. The name can be somewhat misleading, as the first two highly composite numbers (1 and 2) are not actually composite numbers; however, all further terms are. The late mathematician Jean-Pierre Kahane has suggested that Plato must have known about highly composite numbers as he deliberately chose 5040 as the ideal number of citizens in a city as 5040 has more divisors than any numbers less than it. Ramanujan wrote and titled his paper on the subject in 1915. Examples The initial or smallest 38 highly composite numbers are listed in the table below . The number of divisors is given in the column labeled ''d''(''n''). Asterisks indicate superior highly composite numbers. The divisors of the first 15 highly composite ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Prime Number
A prime number (or a prime) is a natural number greater than 1 that is not a product of two smaller natural numbers. A natural number greater than 1 that is not prime is called a composite number. For example, 5 is prime because the only ways of writing it as a product, or , involve 5 itself. However, 4 is composite because it is a product (2 × 2) in which both numbers are smaller than 4. Primes are central in number theory because of the fundamental theorem of arithmetic: every natural number greater than 1 is either a prime itself or can be factorized as a product of primes that is unique up to their order. The property of being prime is called primality. A simple but slow method of checking the primality of a given number n, called trial division, tests whether n is a multiple of any integer between 2 and \sqrt. Faster algorithms include the Miller–Rabin primality test, which is fast but has a small chance of error, and the AKS primality test, which always pr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Strong Pseudoprime
A strong pseudoprime is a composite number that passes the Miller–Rabin primality test. All prime numbers pass this test, but a small fraction of composites also pass, making them "pseudoprimes". Unlike the Fermat pseudoprimes, for which there exist numbers that are pseudoprimes to all coprime bases (the Carmichael numbers), there are no composites that are strong pseudoprimes to all bases. Motivation and first examples Let us say we want to investigate if ''n'' = 31697 is a probable prime (PRP). We pick base ''a'' = 3 and, inspired by Fermat's little theorem, calculate: : 3^ \equiv 1 \pmod This shows 31697 is a Fermat PRP (base 3), so we may suspect it is a prime. We now repeatedly halve the exponent: : 3^ \equiv 1 \pmod : 3^ \equiv 1 \pmod : 3^ \equiv 28419 \pmod The first couple of times do not yield anything interesting (the result was still 1 modulo 31697), but at exponent 3962 we see a result that is neither 1 nor minus 1 (i.e. 31696) modulo 31697. This proves 31697 is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
10,000
10,000 (ten thousand) is the natural number following 9,999 and preceding 10,001. Name Many languages have a specific word for this number: in Ancient Greek it is (the etymological root of the word myriad in English), in Aramaic , in Hebrew [], in Chinese language, Chinese (Mandarin , Cantonese , Hokkien ''bān''), in Japanese language, Japanese [], in Khmer language, Khmer [], in Korean language, Korean [], in Russian language, Russian [], in Vietnamese language, Vietnamese , in Sanskrit अयुत [''ayuta''], in Thai language, Thai [], in Malayalam [], and in Malagasy language, Malagasy ''alina''. In many of these languages, it often denotes a very large but indefinite number. The classical Greeks used letters of the Greek alphabet to represent Greek numerals: they used a capital letter mu (Μ) to represent ten thousand. This Greek root was used in early versions of the metric system in the form of the decimal prefix myria-. The number ten thousand can also be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Erdős–Nicolas Number
In number theory, an Erdős–Nicolas number is a number that is not perfect, but that equals one of the partial sums of its divisors. That is, a number is Erdős–Nicolas number when there exists another number such that : \sum_d=n. The first ten Erdős–Nicolas numbers are : 24, 2016, 8190, 42336, 45864, 392448, 714240, 1571328, 61900800 and 91963648. () They are named after Paul Erdős and Jean-Louis Nicolas, who wrote about them in 1975. See also *Descartes number In number theory, a Descartes number is an odd number which would have been an odd perfect number, if one of its composite factors were prime. They are named after René Descartes who observed that the number would be an odd perfect number if onl ..., another type of almost-perfect numbers References Integer sequences {{numtheory-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Perfect Number
In number theory, a perfect number is a positive integer that is equal to the sum of its positive divisors, excluding the number itself. For instance, 6 has divisors 1, 2 and 3 (excluding itself), and 1 + 2 + 3 = 6, so 6 is a perfect number. The sum of divisors of a number, excluding the number itself, is called its aliquot sum, so a perfect number is one that is equal to its aliquot sum. Equivalently, a perfect number is a number that is half the sum of all of its positive divisors including itself; in symbols, \sigma_1(n)=2n where \sigma_1 is the sum-of-divisors function. For instance, 28 is perfect as 1 + 2 + 4 + 7 + 14 = 28. This definition is ancient, appearing as early as Euclid's ''Elements'' (VII.22) where it is called (''perfect'', ''ideal'', or ''complete number''). Euclid also proved a formation rule (IX.36) whereby q(q+1)/2 is an even perfect number whenever q is a prime of the form 2^p-1 for positive integer p—what is now called a Mersenne prime. Two millennia ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
