21642687 has 16 divisors (see below), whose sum is σ = 34978560. Its totient is φ = 13116600.

The previous prime is 21642667. The next prime is 21642727. The reversal of 21642687 is 78624612.

21642687 is a `hidden beast` number, since 2 + 1 + 642 + 6 + 8 + 7 = 666.

It is not a de Polignac number, because 21642687 - 2⁷ = 21642559 is a prime.

It is a Smith number, since the sum of its digits (36) coincides with the sum of the digits of its prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21642637) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 36139 + ... + 36732.

It is an arithmetic number, because the mean of its divisors is an integer number (2186160).

Almost surely, 2^21642687 is an apocalyptic number.

21642687 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

21642687 is a deficient number, since it is larger than the sum of its proper divisors (13335873).

21642687 is a wasteful number, since it uses less digits than its factorization.

21642687 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 72891 (or 72885 counting only the distinct ones).

The product of its digits is 32256, while the sum is 36.

The square root of 21642687 is about 4652.1701387632. The cubic root of 21642687 is about 278.6786680944.

It can be divided in two parts, 2164 and 2687, that added together give a triangular number (4851 = T₉₈).

The spelling of 21642687 in words is "twenty-one million, six hundred forty-two thousand, six hundred eighty-seven".