81391924 has 24 divisors (see below), whose sum is σ = 145582920. Its totient is φ = 39806976.

The previous prime is 81391909. The next prime is 81391943. The reversal of 81391924 is 42919318.

It can be written as a sum of positive squares in 4 ways, for example, as 67600 + 81324324 = 260^2 + 9018^2 .

It is a congruent number.

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, 33354 + ... + 35710.

It is an arithmetic number, because the mean of its divisors is an integer number (6065955).

Almost surely, 2^81391924 is an apocalyptic number.

It is an amenable number.

81391924 is a deficient number, since it is larger than the sum of its proper divisors (64190996).

81391924 is a wasteful number, since it uses less digits than its factorization.

81391924 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2547 (or 2545 counting only the distinct ones).

The product of its digits is 15552, while the sum is 37.

The square root of 81391924 is about 9021.7472808764. The cubic root of 81391924 is about 433.3715908366.

The spelling of 81391924 in words is "eighty-one million, three hundred ninety-one thousand, nine hundred twenty-four".