21643985 has 16 divisors (see below), whose sum is σ = 28494720. Its totient is φ = 15651840.

The previous prime is 21643967. The next prime is 21644003. The reversal of 21643985 is 58934612.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21643967) and next prime (21644003).

It is not a de Polignac number, because 21643985 - 2⁸ = 21643729 is a prime.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 9596 + ... + 11634.

It is an arithmetic number, because the mean of its divisors is an integer number (1780920).

Almost surely, 2^21643985 is an apocalyptic number.

It is an amenable number.

21643985 is a deficient number, since it is larger than the sum of its proper divisors (6850735).

21643985 is a wasteful number, since it uses less digits than its factorization.

21643985 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2248.

The product of its digits is 51840, while the sum is 38.

The square root of 21643985 is about 4652.3096414577. The cubic root of 21643985 is about 278.6842391476.

The spelling of 21643985 in words is "twenty-one million, six hundred forty-three thousand, nine hundred eighty-five".