81978920 has 32 divisors (see below), whose sum is σ = 194162400. Its totient is φ = 31065408.

The previous prime is 81978917. The next prime is 81978929. The reversal of 81978920 is 2987918.

It is not an unprimeable number, because it can be changed into a prime (81978929) 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, 53174 + ... + 54693.

It is an arithmetic number, because the mean of its divisors is an integer number (6067575).

Almost surely, 2^81978920 is an apocalyptic number.

It is an amenable number.

81978920 is an abundant number, since it is smaller than the sum of its proper divisors (112183480).

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

81978920 is a wasteful number, since it uses less digits than its factorization.

81978920 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 107897 (or 107893 counting only the distinct ones).

The product of its (nonzero) digits is 72576, while the sum is 44.

The square root of 81978920 is about 9054.2211150380. The cubic root of 81978920 is about 434.4109170652.

The spelling of 81978920 in words is "eighty-one million, nine hundred seventy-eight thousand, nine hundred twenty".