81 (number)

Cardinaleighty-oneOrdinal81st
(eighty-first)Factorization3Divisors1, 3, 9, 27, 81Greek numeralΠΑ´Roman numeralLXXXI, lxxxiBinary1010001₂Ternary10000₃Senary213₆Octal121₈Duodecimal69₁₂Hexadecimal51₁₆

81 (eighty-one) is the natural number following 80 and preceding 82.