21515812 has 24 divisors (see below), whose sum is σ = 40018104. Its totient is φ = 10086912.

The previous prime is 21515803. The next prime is 21515831. The reversal of 21515812 is 21851512.

It can be written as a sum of positive squares in 4 ways, for example, as 7257636 + 14258176 = 2694^2 + 3776^2 .

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, 26598 + ... + 27394.

It is an arithmetic number, because the mean of its divisors is an integer number (1667421).

Almost surely, 2^21515812 is an apocalyptic number.

It is an amenable number.

21515812 is a deficient number, since it is larger than the sum of its proper divisors (18502292).

21515812 is a wasteful number, since it uses less digits than its factorization.

21515812 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1215 (or 1213 counting only the distinct ones).

The product of its digits is 800, while the sum is 25.

The square root of 21515812 is about 4638.5139861814. The cubic root of 21515812 is about 278.1330384749.

The spelling of 21515812 in words is "twenty-one million, five hundred fifteen thousand, eight hundred twelve".