81918631 has 4 divisors (see below), whose sum is σ = 86737392. Its totient is φ = 77099872.

The previous prime is 81918589. The next prime is 81918637. The reversal of 81918631 is 13681918.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 81918631 - 2⁹ = 81918119 is a prime.

It is a super-2 number, since 2×81918631² = 13421324209828322, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81918637) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2409355 + ... + 2409388.

It is an arithmetic number, because the mean of its divisors is an integer number (21684348).

Almost surely, 2^81918631 is an apocalyptic number.

81918631 is a deficient number, since it is larger than the sum of its proper divisors (4818761).

81918631 is a wasteful number, since it uses less digits than its factorization.

81918631 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4818760.

The product of its digits is 10368, while the sum is 37.

The square root of 81918631 is about 9050.8911715919. The cubic root of 81918631 is about 434.3043993463.

The spelling of 81918631 in words is "eighty-one million, nine hundred eighteen thousand, six hundred thirty-one".