81615681 has 24 divisors (see below), whose sum is σ = 139723584. Its totient is φ = 46636560.

The previous prime is 81615631. The next prime is 81615713. The reversal of 81615681 is 18651618.

It is not a de Polignac number, because 81615681 - 2⁶ = 81615617 is a prime.

It is a super-2 number, since 2×81615681² = 13322238770187522, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (81615631) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 22290 + ... + 25691.

It is an arithmetic number, because the mean of its divisors is an integer number (5821816).

Almost surely, 2^81615681 is an apocalyptic number.

81615681 is a gapful number since it is divisible by the number (81) formed by its first and last digit.

It is an amenable number.

81615681 is a deficient number, since it is larger than the sum of its proper divisors (58107903).

81615681 is an equidigital number, since it uses as much as digits as its factorization.

81615681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 48003 (or 47991 counting only the distinct ones).

The product of its digits is 11520, while the sum is 36.

The square root of 81615681 is about 9034.1397487531. The cubic root of 81615681 is about 433.7683591185.

The spelling of 81615681 in words is "eighty-one million, six hundred fifteen thousand, six hundred eighty-one".