21563904 has 80 divisors (see below), whose sum is σ = 58433760. Its totient is φ = 7065600.

The previous prime is 21563897. The next prime is 21563923. The reversal of 21563904 is 40936512.

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, 155067 + ... + 155205.

It is an arithmetic number, because the mean of its divisors is an integer number (730422).

Almost surely, 2^21563904 is an apocalyptic number.

21563904 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21563904, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29216880).

21563904 is an abundant number, since it is smaller than the sum of its proper divisors (36869856).

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

21563904 is a wasteful number, since it uses less digits than its factorization.

21563904 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 261 (or 245 counting only the distinct ones).

The product of its (nonzero) digits is 6480, while the sum is 30.

The square root of 21563904 is about 4643.6950804289. The cubic root of 21563904 is about 278.3401113086.

The spelling of 21563904 in words is "twenty-one million, five hundred sixty-three thousand, nine hundred four".