21684690 has 48 divisors (see below), whose sum is σ = 59700888. Its totient is φ = 5442048.

The previous prime is 21684679. The next prime is 21684713. The reversal of 21684690 is 9648612.

It can be written as a sum of positive squares in 4 ways, for example, as 21427641 + 257049 = 4629^2 + 507^2 .

It is a super-2 number, since 2×21684690² = 940451560792200, which contains 22 as substring.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 5557 + ... + 8616.

Almost surely, 2^21684690 is an apocalyptic number.

21684690 is an abundant number, since it is smaller than the sum of its proper divisors (38016198).

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

21684690 is a wasteful number, since it uses less digits than its factorization.

21684690 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14203 (or 14200 counting only the distinct ones).

The product of its (nonzero) digits is 20736, while the sum is 36.

The square root of 21684690 is about 4656.6822953687. The cubic root of 21684690 is about 278.8588332757.

The spelling of 21684690 in words is "twenty-one million, six hundred eighty-four thousand, six hundred ninety".