21857872 has 10 divisors (see below), whose sum is σ = 42349658. Its totient is φ = 10928928.

The previous prime is 21857863. The next prime is 21857873. The reversal of 21857872 is 27875812.

It can be written as a sum of positive squares in only one way, i.e., 21752896 + 104976 = 4664^2 + 324^2 .

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21857873) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 683043 + ... + 683074.

Almost surely, 2^21857872 is an apocalyptic number.

It is an amenable number.

21857872 is a deficient number, since it is larger than the sum of its proper divisors (20491786).

21857872 is a wasteful number, since it uses less digits than its factorization.

21857872 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1366125 (or 1366119 counting only the distinct ones).

The product of its digits is 62720, while the sum is 40.

The square root of 21857872 is about 4675.2403146790. The cubic root of 21857872 is about 279.5992225400.

The spelling of 21857872 in words is "twenty-one million, eight hundred fifty-seven thousand, eight hundred seventy-two".