21643656 has 16 divisors (see below), whose sum is σ = 54109200. Its totient is φ = 7214544.

The previous prime is 21643607. The next prime is 21643691. The reversal of 21643656 is 65634612.

It is a super-3 number, since 3×21643656³ (a number of 23 digits) contains 333 as substring.

It is a hoax number, since the sum of its digits (33) coincides with the sum of the digits of its distinct prime factors.

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, 450886 + ... + 450933.

It is an arithmetic number, because the mean of its divisors is an integer number (3381825).

Almost surely, 2^21643656 is an apocalyptic number.

It is an amenable number.

21643656 is an abundant number, since it is smaller than the sum of its proper divisors (32465544).

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

21643656 is a wasteful number, since it uses less digits than its factorization.

21643656 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 901828 (or 901824 counting only the distinct ones).

The product of its digits is 25920, while the sum is 33.

The square root of 21643656 is about 4652.2742825418. The cubic root of 21643656 is about 278.6828270913.

The spelling of 21643656 in words is "twenty-one million, six hundred forty-three thousand, six hundred fifty-six".