21128868 has 36 divisors (see below), whose sum is σ = 53703468. Its totient is φ = 7004160.

The previous prime is 21128851. The next prime is 21128869. The reversal of 21128868 is 86882112.

It can be written as a sum of positive squares in 2 ways, for example, as 14379264 + 6749604 = 3792^2 + 2598^2 .

It is a tau number, because it is divible by the number of its divisors (36).

It is a super-2 number, since 2×21128868² = 892858125922848, which contains 22 as substring.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21128869) 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, 5428 + ... + 8468.

It is an arithmetic number, because the mean of its divisors is an integer number (1491763).

Almost surely, 2^21128868 is an apocalyptic number.

It is an amenable number.

21128868 is an abundant number, since it is smaller than the sum of its proper divisors (32574600).

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

21128868 is a wasteful number, since it uses less digits than its factorization.

21128868 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3244 (or 3239 counting only the distinct ones).

The product of its digits is 12288, while the sum is 36.

The square root of 21128868 is about 4596.6148413806. The cubic root of 21128868 is about 276.4556116866.

The spelling of 21128868 in words is "twenty-one million, one hundred twenty-eight thousand, eight hundred sixty-eight".