81615631 has 2 divisors, whose sum is σ = 81615632. Its totient is φ = 81615630.

The previous prime is 81615629. The next prime is 81615713. The reversal of 81615631 is 13651618.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 81615631 - 2¹ = 81615629 is a prime.

It is a super-2 number, since 2×81615631² = 13322222447056322, which contains 22 as substring.

Together with 81615629, it forms a pair of twin primes.

It is equal to p_4758322 and since 81615631 and 4758322 have the same sum of digits, it is a Honaker prime.

It is a junction number, because it is equal to n+sod(n) for n = 81615593 and 81615602.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (81615031) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 40807815 + 40807816.

It is an arithmetic number, because the mean of its divisors is an integer number (40807816).

Almost surely, 2^81615631 is an apocalyptic number.

81615631 is a deficient number, since it is larger than the sum of its proper divisors (1).

81615631 is an equidigital number, since it uses as much as digits as its factorization.

81615631 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4320, while the sum is 31.

The square root of 81615631 is about 9034.1369814720. The cubic root of 81615631 is about 433.7682705390.

The spelling of 81615631 in words is "eighty-one million, six hundred fifteen thousand, six hundred thirty-one".