21329664 has 36 divisors (see below), whose sum is σ = 56770056. Its totient is φ = 7109632.

The previous prime is 21329663. The next prime is 21329683. The reversal of 21329664 is 46692312.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21329663) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 13119 + ... + 14654.

It is an arithmetic number, because the mean of its divisors is an integer number (1576946).

Almost surely, 2^21329664 is an apocalyptic number.

21329664 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21329664 is an abundant number, since it is smaller than the sum of its proper divisors (35440392).

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

21329664 is an equidigital number, since it uses as much as digits as its factorization.

21329664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 27792 (or 27778 counting only the distinct ones).

The product of its digits is 15552, while the sum is 33.

The square root of 21329664 is about 4618.4049194500. The cubic root of 21329664 is about 277.3286077433.

The spelling of 21329664 in words is "twenty-one million, three hundred twenty-nine thousand, six hundred sixty-four".