21636864 has 54 divisors (see below), whose sum is σ = 62391056. Its totient is φ = 7211520.

The previous prime is 21636851. The next prime is 21636887. The reversal of 21636864 is 46863612.

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

It is a nude number because it is divisible by every one of its digits.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 2392 + ... + 6999.

Almost surely, 2^21636864 is an apocalyptic number.

21636864 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21636864 is an abundant number, since it is smaller than the sum of its proper divisors (40754192).

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

21636864 is an equidigital number, since it uses as much as digits as its factorization.

21636864 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9413 (or 9396 counting only the distinct ones).

The product of its digits is 41472, while the sum is 36.

The square root of 21636864 is about 4651.5442597056. The cubic root of 21636864 is about 278.6536728703.

Adding to 21636864 its product of digits (41472), we get a square (21678336 = 4656²).

It can be divided in two parts, 21636 and 864, that added together give a square (22500 = 150²).

The spelling of 21636864 in words is "twenty-one million, six hundred thirty-six thousand, eight hundred sixty-four".