21105864 has 48 divisors (see below), whose sum is σ = 61561500. Its totient is φ = 6493824.

The previous prime is 21105863. The next prime is 21105907. The reversal of 21105864 is 46850112.

It can be written as a sum of positive squares in 2 ways, for example, as 20629764 + 476100 = 4542^2 + 690^2 .

It is not an unprimeable number, because it can be changed into a prime (21105863) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 10339 + ... + 12210.

Almost surely, 2^21105864 is an apocalyptic number.

21105864 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

21105864 is an abundant number, since it is smaller than the sum of its proper divisors (40455636).

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

21105864 is a wasteful number, since it uses less digits than its factorization.

21105864 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22574 (or 22567 counting only the distinct ones).

The product of its (nonzero) digits is 1920, while the sum is 27.

The square root of 21105864 is about 4594.1118837051. Note that the first 3 decimals coincide. The cubic root of 21105864 is about 276.3552451442.

Adding to 21105864 its reverse (46850112), we get a palindrome (67955976).

The spelling of 21105864 in words is "twenty-one million, one hundred five thousand, eight hundred sixty-four".