21686680 has 16 divisors (see below), whose sum is σ = 48795120. Its totient is φ = 8674656.

The previous prime is 21686671. The next prime is 21686741. The reversal of 21686680 is 8668612.

It is a congruent number.

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, 271044 + ... + 271123.

It is an arithmetic number, because the mean of its divisors is an integer number (3049695).

Almost surely, 2^21686680 is an apocalyptic number.

21686680 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21686680 is an abundant number, since it is smaller than the sum of its proper divisors (27108440).

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

21686680 is a wasteful number, since it uses less digits than its factorization.

21686680 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 542178 (or 542174 counting only the distinct ones).

The product of its (nonzero) digits is 27648, while the sum is 37.

The square root of 21686680 is about 4656.8959619042. The cubic root of 21686680 is about 278.8673632893.

It can be divided in two parts, 21686 and 680, that added together give a triangular number (22366 = T₂₁₁).

The spelling of 21686680 in words is "twenty-one million, six hundred eighty-six thousand, six hundred eighty".