21684686 has 8 divisors (see below), whose sum is σ = 33576384. Its totient is φ = 10492560.

The previous prime is 21684679. The next prime is 21684713. The reversal of 21684686 is 68648612.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 174815 + ... + 174938.

It is an arithmetic number, because the mean of its divisors is an integer number (4197048).

Almost surely, 2^21684686 is an apocalyptic number.

21684686 is a deficient number, since it is larger than the sum of its proper divisors (11891698).

21684686 is a wasteful number, since it uses less digits than its factorization.

21684686 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 349786.

The product of its digits is 110592, while the sum is 41.

The square root of 21684686 is about 4656.6818658783. The cubic root of 21684686 is about 278.8588161294.

It can be divided in two parts, 216 and 84686, that multiplied together give a triangular number (18292176 = T₆₀₄₈).

The spelling of 21684686 in words is "twenty-one million, six hundred eighty-four thousand, six hundred eighty-six".