21664736 has 24 divisors (see below), whose sum is σ = 43137360. Its totient is φ = 10709248.

The previous prime is 21664729. The next prime is 21664739. The reversal of 21664736 is 63746612.

It is a junction number, because it is equal to n+sod(n) for n = 21664696 and 21664705.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21664739) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 956 + ... + 6651.

It is an arithmetic number, because the mean of its divisors is an integer number (1797390).

Almost surely, 2^21664736 is an apocalyptic number.

It is an amenable number.

21664736 is a deficient number, since it is larger than the sum of its proper divisors (21472624).

21664736 is an equidigital number, since it uses as much as digits as its factorization.

21664736 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7706 (or 7698 counting only the distinct ones).

The product of its digits is 36288, while the sum is 35.

The square root of 21664736 is about 4654.5392897686. The cubic root of 21664736 is about 278.7732728060.

The spelling of 21664736 in words is "twenty-one million, six hundred sixty-four thousand, seven hundred thirty-six".