Factors / Factors of 81

Factors of 81

1, 3, 9, 27, 81

81 is a perfect square (9² = 81); that gives 81 an odd 5-divisor count, since only 9 pairs with itself. 81's full pair list is (1, 81), (3, 27), (9, 9), for 5 divisors in total. 81's divisors other than 81 itself sum to just 40, 41 below 81: the common deficient case. 81 is odd, digit sum 9 for 81; small divisors of 81 include 3, 9. 81 has 5 divisors; 80 has 10 and 82 has 4, so 80 wins here. 81 divided by its largest divisor, 27, gives 3.