21316815 has 36 divisors (see below), whose sum is σ = 40024296. Its totient is φ = 10490688.

The previous prime is 21316783. The next prime is 21316819. The reversal of 21316815 is 51861312.

It is not a de Polignac number, because 21316815 - 2⁵ = 21316783 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21316819) by changing a digit.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 6204 + ... + 9006.

It is an arithmetic number, because the mean of its divisors is an integer number (1111786).

Almost surely, 2^21316815 is an apocalyptic number.

21316815 is a deficient number, since it is larger than the sum of its proper divisors (18707481).

21316815 is a wasteful number, since it uses less digits than its factorization.

21316815 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2840 (or 2824 counting only the distinct ones).

The product of its digits is 1440, while the sum is 27.

The square root of 21316815 is about 4617.0136452040. The cubic root of 21316815 is about 277.2729089279.

The spelling of 21316815 in words is "twenty-one million, three hundred sixteen thousand, eight hundred fifteen".