21664988 has 12 divisors (see below), whose sum is σ = 39562320. Its totient is φ = 10361472.

The previous prime is 21664967. The next prime is 21665009. The reversal of 21664988 is 88946612.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21664967) and next prime (21665009).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 117653 + ... + 117836.

It is an arithmetic number, because the mean of its divisors is an integer number (3296860).

Almost surely, 2^21664988 is an apocalyptic number.

It is an amenable number.

21664988 is a deficient number, since it is larger than the sum of its proper divisors (17897332).

21664988 is a wasteful number, since it uses less digits than its factorization.

21664988 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 235516 (or 235514 counting only the distinct ones).

The product of its digits is 165888, while the sum is 44.

The square root of 21664988 is about 4654.5663600383. The cubic root of 21664988 is about 278.7743536807.

The spelling of 21664988 in words is "twenty-one million, six hundred sixty-four thousand, nine hundred eighty-eight".