21515391 has 12 divisors (see below), whose sum is σ = 32713720. Its totient is φ = 13588560.

The previous prime is 21515381. The next prime is 21515411. The reversal of 21515391 is 19351512.

It is not a de Polignac number, because 21515391 - 2⁵ = 21515359 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 (21515321) 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 11 ways as a sum of consecutive naturals, for example, 62740 + ... + 63081.

Almost surely, 2^21515391 is an apocalyptic number.

21515391 is a deficient number, since it is larger than the sum of its proper divisors (11198329).

21515391 is a wasteful number, since it uses less digits than its factorization.

21515391 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 125846 (or 125843 counting only the distinct ones).

The product of its digits is 1350, while the sum is 27.

The square root of 21515391 is about 4638.4686050463. The cubic root of 21515391 is about 278.1312243862.

The spelling of 21515391 in words is "twenty-one million, five hundred fifteen thousand, three hundred ninety-one".