81905812 has 12 divisors (see below), whose sum is σ = 144164916. Its totient is φ = 40715840.

The previous prime is 81905809. The next prime is 81905821. The reversal of 81905812 is 21850918.

It can be written as a sum of positive squares in 2 ways, for example, as 79637776 + 2268036 = 8924^2 + 1506^2 .

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 58489 + ... + 59872.

It is an arithmetic number, because the mean of its divisors is an integer number (12013743).

Almost surely, 2^81905812 is an apocalyptic number.

It is an amenable number.

81905812 is a deficient number, since it is larger than the sum of its proper divisors (62259104).

81905812 is a wasteful number, since it uses less digits than its factorization.

81905812 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 118538 (or 118536 counting only the distinct ones).

The product of its (nonzero) digits is 5760, while the sum is 34.

The square root of 81905812 is about 9050.1829815756. The cubic root of 81905812 is about 434.2817441886.

The spelling of 81905812 in words is "eighty-one million, nine hundred five thousand, eight hundred twelve".