81307820 has 24 divisors (see below), whose sum is σ = 186269328. Its totient is φ = 29566400.

The previous prime is 81307801. The next prime is 81307847. The reversal of 81307820 is 2870318.

It is a super-2 number, since 2×81307820² = 13221923186304800, which contains 22 as substring.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 184571 + ... + 185010.

It is an arithmetic number, because the mean of its divisors is an integer number (7761222).

Almost surely, 2^81307820 is an apocalyptic number.

It is an amenable number.

81307820 is an abundant number, since it is smaller than the sum of its proper divisors (104961508).

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

81307820 is a wasteful number, since it uses less digits than its factorization.

81307820 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 369601 (or 369599 counting only the distinct ones).

The product of its (nonzero) digits is 2688, while the sum is 29.

The square root of 81307820 is about 9017.0848947983. The cubic root of 81307820 is about 433.2222687092. Note that the first 4 decimals are identical.

The spelling of 81307820 in words is "eighty-one million, three hundred seven thousand, eight hundred twenty".