21691664 has 20 divisors (see below), whose sum is σ = 42159504. Its totient is φ = 10811808.

The previous prime is 21691633. The next prime is 21691693. The reversal of 21691664 is 46619612.

It is a hoax number, since the sum of its digits (35) coincides with the sum of the digits of its distinct prime factors.

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, 3599 + ... + 7505.

Almost surely, 2^21691664 is an apocalyptic number.

It is an amenable number.

21691664 is a deficient number, since it is larger than the sum of its proper divisors (20467840).

21691664 is a wasteful number, since it uses less digits than its factorization.

21691664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4262 (or 4256 counting only the distinct ones).

The product of its digits is 15552, while the sum is 35.

The square root of 21691664 is about 4657.4310515562. The cubic root of 21691664 is about 278.8887246116. Note that the first 3 decimals are identical.

The spelling of 21691664 in words is "twenty-one million, six hundred ninety-one thousand, six hundred sixty-four".