81975621 has 16 divisors (see below), whose sum is σ = 134524544. Its totient is φ = 43239744.

The previous prime is 81975613. The next prime is 81975623. The reversal of 81975621 is 12657918.

It is not a de Polignac number, because 81975621 - 2³ = 81975613 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (39).

It is a self number, because there is not a number n which added to its sum of digits gives 81975621.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81975623) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 149866 + ... + 150411.

It is an arithmetic number, because the mean of its divisors is an integer number (8407784).

Almost surely, 2^81975621 is an apocalyptic number.

It is an amenable number.

81975621 is a deficient number, since it is larger than the sum of its proper divisors (52548923).

81975621 is a wasteful number, since it uses less digits than its factorization.

81975621 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 300300.

The product of its digits is 30240, while the sum is 39.

The square root of 81975621 is about 9054.0389329845. The cubic root of 81975621 is about 434.4050897914.

The spelling of 81975621 in words is "eighty-one million, nine hundred seventy-five thousand, six hundred twenty-one".