81631820 has 24 divisors (see below), whose sum is σ = 175609728. Its totient is φ = 31856000.

The previous prime is 81631817. The next prime is 81631829. The reversal of 81631820 is 2813618.

It is not an unprimeable number, because it can be changed into a prime (81631829) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 48956 + ... + 50595.

It is an arithmetic number, because the mean of its divisors is an integer number (7317072).

Almost surely, 2^81631820 is an apocalyptic number.

It is an amenable number.

81631820 is an abundant number, since it is smaller than the sum of its proper divisors (93977908).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

81631820 is a wasteful number, since it uses less digits than its factorization.

81631820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 99601 (or 99599 counting only the distinct ones).

The product of its (nonzero) digits is 2304, while the sum is 29.

The square root of 81631820 is about 9035.0329274441. The cubic root of 81631820 is about 433.7969489110.

The spelling of 81631820 in words is "eighty-one million, six hundred thirty-one thousand, eight hundred twenty".