21815964 has 72 divisors (see below), whose sum is σ = 59819760. Its totient is φ = 6676992.

The previous prime is 21815939. The next prime is 21815987. The reversal of 21815964 is 46951812.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 25902 + ... + 26730.

It is an arithmetic number, because the mean of its divisors is an integer number (830830).

Almost surely, 2^21815964 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21815964, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29909880).

21815964 is an abundant number, since it is smaller than the sum of its proper divisors (38003796).

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

21815964 is a wasteful number, since it uses less digits than its factorization.

21815964 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 899 (or 894 counting only the distinct ones).

The product of its digits is 17280, while the sum is 36.

The square root of 21815964 is about 4670.7562556828. The cubic root of 21815964 is about 279.4204167715.

The spelling of 21815964 in words is "twenty-one million, eight hundred fifteen thousand, nine hundred sixty-four".