81239521 has 6 divisors (see below), whose sum is σ = 89296466. Its totient is φ = 73854000.

The previous prime is 81239507. The next prime is 81239533. The reversal of 81239521 is 12593218.

It can be written as a sum of positive squares in only one way, i.e., 73616400 + 7623121 = 8580^2 + 2761^2 .

It is not a de Polignac number, because 81239521 - 2⁵ = 81239489 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (81239021) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 335580 + ... + 335821.

Almost surely, 2^81239521 is an apocalyptic number.

It is an amenable number.

81239521 is a deficient number, since it is larger than the sum of its proper divisors (8056945).

81239521 is a wasteful number, since it uses less digits than its factorization.

81239521 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 671423 (or 671412 counting only the distinct ones).

The product of its digits is 4320, while the sum is 31.

The square root of 81239521 is about 9013.2968995812. The cubic root of 81239521 is about 433.1009317272.

The spelling of 81239521 in words is "eighty-one million, two hundred thirty-nine thousand, five hundred twenty-one".