**81 (number) - Wikipedia**
https://en.wikipedia.org/wiki/81_(number)

WebIn mathematics 81 is: the square of 9 and the second fourth-power of a prime; 3 4. with an aliquot sum of 40; within an aliquot sequence of three composite numbers (81, 40, 50, 43, 1 ,0) to the Prime in the 43 -aliquot tree. a perfect totient number like all powers of three. [1] a heptagonal number. [2] an icosioctagonal number. [3]

**DA:** 48 **PA:** 42 **MOZ Rank:** 78