21391664 has 20 divisors (see below), whose sum is σ = 47367504. Its totient is φ = 9167808.

The previous prime is 21391651. The next prime is 21391703. The reversal of 21391664 is 46619312.

It is a self number, because there is not a number n which added to its sum of digits gives 21391664.

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, 95387 + ... + 95610.

Almost surely, 2^21391664 is an apocalyptic number.

It is an amenable number.

21391664 is an abundant number, since it is smaller than the sum of its proper divisors (25975840).

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

21391664 is a wasteful number, since it uses less digits than its factorization.

21391664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 191012 (or 191006 counting only the distinct ones).

The product of its digits is 7776, while the sum is 32.

The square root of 21391664 is about 4625.1123229604. The cubic root of 21391664 is about 277.5970561135.

The spelling of 21391664 in words is "twenty-one million, three hundred ninety-one thousand, six hundred sixty-four".