81939564 has 54 divisors (see below), whose sum is σ = 240946524. Its totient is φ = 23410800.

The previous prime is 81939503. The next prime is 81939569. The reversal of 81939564 is 46593918.

It is a happy number.

81939564 is a `hidden beast` number, since 81 + 9 + 3 + 9 + 564 = 666.

It is not an unprimeable number, because it can be changed into a prime (81939569) by changing a digit.

It is a polite number, since it can be written in 17 ways as a sum of consecutive naturals, for example, 21462 + ... + 24989.

Almost surely, 2^81939564 is an apocalyptic number.

81939564 is a gapful number since it is divisible by the number (84) formed by its first and last digit.

It is an amenable number.

81939564 is an abundant number, since it is smaller than the sum of its proper divisors (159006960).

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

81939564 is a wasteful number, since it uses less digits than its factorization.

81939564 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 46475 (or 46463 counting only the distinct ones).

The product of its digits is 233280, while the sum is 45.

The square root of 81939564 is about 9052.0475031895. The cubic root of 81939564 is about 434.3413893839.

The spelling of 81939564 in words is "eighty-one million, nine hundred thirty-nine thousand, five hundred sixty-four".