21557128 has 8 divisors (see below), whose sum is σ = 40419630. Its totient is φ = 10778560.

The previous prime is 21557113. The next prime is 21557143. The reversal of 21557128 is 82175512.

It is an interprime number because it is at equal distance from previous prime (21557113) and next prime (21557143).

It can be written as a sum of positive squares in only one way, i.e., 11710084 + 9847044 = 3422^2 + 3138^2 .

It is a tau number, because it is divible by the number of its divisors (8).

It is a self number, because there is not a number n which added to its sum of digits gives 21557128.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 1347313 + ... + 1347328.

Almost surely, 2^21557128 is an apocalyptic number.

It is an amenable number.

21557128 is a deficient number, since it is larger than the sum of its proper divisors (18862502).

21557128 is a wasteful number, since it uses less digits than its factorization.

21557128 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2694647 (or 2694643 counting only the distinct ones).

The product of its digits is 5600, while the sum is 31.

The square root of 21557128 is about 4642.9654317042. The cubic root of 21557128 is about 278.3109540933.

The spelling of 21557128 in words is "twenty-one million, five hundred fifty-seven thousand, one hundred twenty-eight".