21643875 has 96 divisors (see below), whose sum is σ = 44815680. Its totient is φ = 10296000.

The previous prime is 21643849. The next prime is 21643877. The reversal of 21643875 is 57834612.

21643875 is a `hidden beast` number, since 2 + 1 + 643 + 8 + 7 + 5 = 666.

It is not a de Polignac number, because 21643875 - 2¹⁰ = 21642851 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.

Its product of digits (40320) is a multiple of the sum of its prime divisors (72).

It is not an unprimeable number, because it can be changed into a prime (21643877) by changing a digit.

It is a polite number, since it can be written in 95 ways as a sum of consecutive naturals, for example, 408349 + ... + 408401.

It is an arithmetic number, because the mean of its divisors is an integer number (466830).

Almost surely, 2^21643875 is an apocalyptic number.

21643875 is a gapful number since it is divisible by the number (25) formed by its first and last digit.

21643875 is an abundant number, since it is smaller than the sum of its proper divisors (23171805).

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

21643875 is a wasteful number, since it uses less digits than its factorization.

21643875 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 99 (or 72 counting only the distinct ones).

The product of its digits is 40320, while the sum is 36.

The square root of 21643875 is about 4652.2978193577. The cubic root of 21643875 is about 278.6837670331.

The spelling of 21643875 in words is "twenty-one million, six hundred forty-three thousand, eight hundred seventy-five".