78 (seventy-eight) is the
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 n ...
following
77 and followed by
79.
In mathematics
78 is:
*the dimension of the
exceptional Lie group
E6 and several related objects.
*a
sphenic number
In number theory, a sphenic number (from grc, σφήνα, 'wedge') is a positive integer that is the product of three distinct prime numbers. Because there are infinitely many prime numbers, there are also infinitely many sphenic numbers.
Definit ...
, having 3 distinct prime
factors
Factor, a Latin word meaning "who/which acts", may refer to:
Commerce
* Factor (agent), a person who acts for, notably a mercantile and colonial agent
* Factor (Scotland), a person or firm managing a Scottish estate
* Factors of production, suc ...
.
*an
abundant number
In number theory, an abundant number or excessive number is a number for which the sum of its proper divisors is greater than the number. The integer 12 is the first abundant number. Its proper divisors are 1, 2, 3, 4 and 6 for a total of 16. Th ...
with an aliquot sum of 90.
*a
semiperfect number
In number theory, a semiperfect number or pseudoperfect number is a natural number ''n'' that is equal to the sum of all or some of its proper divisors. A semiperfect number that is equal to the sum of all its proper divisors is a perfect number.
...
, as a multiple of a perfect number.
*the 12th
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 ...
.
*a
palindromic number
A palindromic number (also known as a numeral palindrome or a numeric palindrome) is a number (such as 16461) that remains the same when its digits are reversed. In other words, it has reflectional symmetry across a vertical axis. The term ''palin ...
in bases 5 (303
5), 7 (141
7), 12 (66
12), 25 (33
25), and 38 (22
38).
*a
Harshad number
In mathematics, a harshad number (or Niven number) in a given number base is an integer that is divisible by the sum of its digits when written in that base.
Harshad numbers in base are also known as -harshad (or -Niven) numbers.
Harshad numbers ...
in bases 3, 4, 5, 6, 7, 13 and 14.
*an
Erdős–Woods number In number theory, a positive integer is said to be an Erdős–Woods number if it has the following property:
there exists a positive integer such that in the sequence of consecutive integers, each of the elements has a non-trivial common factor ...
, since it is possible to find sequences of 78 consecutive integers such that each inner member shares a factor with either the first or the last member.
77 and 78 form a
Ruth-Aaron pair.
In science
*The
atomic number
The atomic number or nuclear charge number (symbol ''Z'') of a chemical element is the charge number of an atomic nucleus. For ordinary nuclei, this is equal to the proton number (''n''p) or the number of protons found in the nucleus of every ...
of
platinum
Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver".
Platinu ...
.
In other fields
78 is also:
*In reference to
gramophone record
A phonograph record (also known as a gramophone record, especially in British English), or simply a record, is an analog sound storage medium in the form of a flat disc with an inscribed, modulated spiral groove. The groove usually starts nea ...
s, 78 refers those meant to be spun at 78
revolutions per minute
Revolutions per minute (abbreviated rpm, RPM, rev/min, r/min, or with the notation min−1) is a unit of rotational speed or rotational frequency for rotating machines.
Standards
ISO 80000-3:2019 defines a unit of rotation as the dimensionl ...
. Compare:
LP, and
45 rpm. 33 + 45 = 78
*A typical
tarot
The tarot (, first known as '' trionfi'' and later as ''tarocchi'' or ''tarocks'') is a pack of playing cards, used from at least the mid-15th century in various parts of Europe to play card games such as Tarocchini. From their Italian roots, ...
deck containing the 21
trump cards
A trump is a playing card which is elevated above its usual rank in trick-taking games. Typically, an entire suit is nominated as a ''trump suit''; these cards then outrank all cards of plain (non-trump) suits. In other contexts, the terms ''tru ...
, the
Fool
Fool, The Fool, or Fools may refer to:
*A jester, also called a ''fool'', a type of historical entertainer known for their witty jokes
*An insult referring to someone of low intelligence or easy gullibility Arts, entertainment and media Fictio ...
and the 56 suit cards make up 78 cards
*The
Rule of 78s is a method of yearly interest calculation
References
{{Integers, zero
Integers