21881864 has 16 divisors (see below), whose sum is σ = 42029820. Its totient is φ = 10673920.

The previous prime is 21881857. The next prime is 21881891. The reversal of 21881864 is 46818812.

It can be written as a sum of positive squares in 2 ways, for example, as 21696964 + 184900 = 4658^2 + 430^2 .

It is a super-2 number, since 2×21881864² = 957631944228992, which contains 22 as substring.

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, 33029 + ... + 33684.

Almost surely, 2^21881864 is an apocalyptic number.

It is an amenable number.

21881864 is a deficient number, since it is larger than the sum of its proper divisors (20147956).

21881864 is a wasteful number, since it uses less digits than its factorization.

21881864 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 66760 (or 66756 counting only the distinct ones).

The product of its digits is 24576, while the sum is 38.

The square root of 21881864 is about 4677.8054683794. The cubic root of 21881864 is about 279.7014845790.

The spelling of 21881864 in words is "twenty-one million, eight hundred eighty-one thousand, eight hundred sixty-four".