81691431 has 16 divisors (see below), whose sum is σ = 115165440. Its totient is φ = 51364800.

The previous prime is 81691427. The next prime is 81691433. The reversal of 81691431 is 13419618.

It is not a de Polignac number, because 81691431 - 2² = 81691427 is a prime.

It is a super-2 number, since 2×81691431² = 13346979797655522, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 81691392 and 81691401.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81691433) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 10206 + ... + 16356.

It is an arithmetic number, because the mean of its divisors is an integer number (7197840).

Almost surely, 2^81691431 is an apocalyptic number.

81691431 is a deficient number, since it is larger than the sum of its proper divisors (33474009).

81691431 is a wasteful number, since it uses less digits than its factorization.

81691431 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6406.

The product of its digits is 5184, while the sum is 33.

The square root of 81691431 is about 9038.3312065890. The cubic root of 81691431 is about 433.9025154985.

The spelling of 81691431 in words is "eighty-one million, six hundred ninety-one thousand, four hundred thirty-one".