21581664 has 48 divisors (see below), whose sum is σ = 61013232. Its totient is φ = 6640128.

The previous prime is 21581641. The next prime is 21581671. The reversal of 21581664 is 46618512.

It is a tau number, because it is divible by the number of its divisors (48).

It is a congruent number.

It is an unprimeable number.

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 7 ways as a sum of consecutive naturals, for example, 7399 + ... + 9894.

It is an arithmetic number, because the mean of its divisors is an integer number (1271109).

Almost surely, 2^21581664 is an apocalyptic number.

21581664 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21581664 is an abundant number, since it is smaller than the sum of its proper divisors (39431568).

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

21581664 is a wasteful number, since it uses less digits than its factorization.

21581664 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 17319 (or 17311 counting only the distinct ones).

The product of its digits is 11520, while the sum is 33.

The square root of 21581664 is about 4645.6069571155. The cubic root of 21581664 is about 278.4165038439.

The spelling of 21581664 in words is "twenty-one million, five hundred eighty-one thousand, six hundred sixty-four".