21657684 has 24 divisors (see below), whose sum is σ = 51364768. Its totient is φ = 7100640.

The previous prime is 21657667. The next prime is 21657689. The reversal of 21657684 is 48675612.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21657689) 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 7 ways as a sum of consecutive naturals, for example, 14062 + ... + 15525.

Almost surely, 2^21657684 is an apocalyptic number.

It is an amenable number.

21657684 is an abundant number, since it is smaller than the sum of its proper divisors (29707084).

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

21657684 is a wasteful number, since it uses less digits than its factorization.

21657684 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 29655 (or 29653 counting only the distinct ones).

The product of its digits is 80640, while the sum is 39.

The square root of 21657684 is about 4653.7816880468. The cubic root of 21657684 is about 278.7430220726.

The spelling of 21657684 in words is "twenty-one million, six hundred fifty-seven thousand, six hundred eighty-four".