21615816 has 16 divisors (see below), whose sum is σ = 54039600. Its totient is φ = 7205264.

The previous prime is 21615809. The next prime is 21615851. The reversal of 21615816 is 61851612.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 450306 + ... + 450353.

It is an arithmetic number, because the mean of its divisors is an integer number (3377475).

Almost surely, 2^21615816 is an apocalyptic number.

It is an amenable number.

21615816 is an abundant number, since it is smaller than the sum of its proper divisors (32423784).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21615816 is a wasteful number, since it uses less digits than its factorization.

21615816 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 900668 (or 900664 counting only the distinct ones).

The product of its digits is 2880, while the sum is 30.

The square root of 21615816 is about 4649.2812347717. The cubic root of 21615816 is about 278.5632869228.

The spelling of 21615816 in words is "twenty-one million, six hundred fifteen thousand, eight hundred sixteen".