81975564 has 216 divisors, whose sum is σ = 256196304. Its totient is φ = 22809600.

The previous prime is 81975559. The next prime is 81975571. The reversal of 81975564 is 46557918.

81975564 is a `hidden beast` number, since 8 + 1 + 97 + 556 + 4 = 666.

It is an unprimeable number.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 1999384 + ... + 1999424.

It is an arithmetic number, because the mean of its divisors is an integer number (1186094).

Almost surely, 2^81975564 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 81975564, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (128098152).

81975564 is an abundant number, since it is smaller than the sum of its proper divisors (174220740).

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

81975564 is a wasteful number, since it uses less digits than its factorization.

81975564 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 99 (or 74 counting only the distinct ones).

The product of its digits is 302400, while the sum is 45.

The square root of 81975564 is about 9054.0357852176. The cubic root of 81975564 is about 434.4049891066.

The spelling of 81975564 in words is "eighty-one million, nine hundred seventy-five thousand, five hundred sixty-four".