21708684 has 36 divisors (see below), whose sum is σ = 55027336. Its totient is φ = 7216128.

The previous prime is 21708671. The next prime is 21708703. The reversal of 21708684 is 48680712.

It is a tau number, because it is divible by the number of its divisors (36).

It is a super-2 number, since 2×21708684² = 942533922023712, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is an unprimeable number.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 18252 + ... + 19404.

Almost surely, 2^21708684 is an apocalyptic number.

It is an amenable number.

21708684 is an abundant number, since it is smaller than the sum of its proper divisors (33318652).

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

21708684 is a wasteful number, since it uses less digits than its factorization.

21708684 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1686 (or 1681 counting only the distinct ones).

The product of its (nonzero) digits is 21504, while the sum is 36.

The square root of 21708684 is about 4659.2578808218. The cubic root of 21708684 is about 278.9616473276.

The spelling of 21708684 in words is "twenty-one million, seven hundred eight thousand, six hundred eighty-four".