81856631 has 4 divisors (see below), whose sum is σ = 82104264. Its totient is φ = 81609000.

The previous prime is 81856603. The next prime is 81856661. The reversal of 81856631 is 13665818.

It is a happy number.

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 81856631 - 2¹⁰ = 81855607 is a prime.

It is a super-2 number, since 2×81856631² = 13401016077340322, 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 (81856661) 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, 123320 + ... + 123981.

It is an arithmetic number, because the mean of its divisors is an integer number (20526066).

Almost surely, 2^81856631 is an apocalyptic number.

81856631 is a deficient number, since it is larger than the sum of its proper divisors (247633).

81856631 is a wasteful number, since it uses less digits than its factorization.

81856631 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 247632.

The product of its digits is 34560, while the sum is 38.

The square root of 81856631 is about 9047.4654461899. The cubic root of 81856631 is about 434.1948041359.

The spelling of 81856631 in words is "eighty-one million, eight hundred fifty-six thousand, six hundred thirty-one".