# 81 (number)

81 is the natural number following 80 and preceding 82.

 List of numbers — Integers << 80 81 82 83 84 85 86 87 88 89 >>
Cardinaleighty-one
Ordinal81st (eighty-first)
Factorization[itex]3^4[itex]
Divisors 3, 9, 27
Roman numeralLXXXI
Binary01010001

## In mathematics

Eighty-one is a square, a heptagonal number and a centered octagonal number. It is also a tribonacci number, an open meandric number and a Harshad number.

## In other fields

Eighty-one is also:

es:Ochenta y uno

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