21398557 has 2 divisors, whose sum is σ = 21398558. Its totient is φ = 21398556.

The previous prime is 21398521. The next prime is 21398561. The reversal of 21398557 is 75589312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21288996 + 109561 = 4614^2 + 331^2 .

It is a cyclic number.

It is not a de Polignac number, because 21398557 - 2²³ = 13009949 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21398957) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10699278 + 10699279.

It is an arithmetic number, because the mean of its divisors is an integer number (10699279).

Almost surely, 2^21398557 is an apocalyptic number.

It is an amenable number.

21398557 is a deficient number, since it is larger than the sum of its proper divisors (1).

21398557 is an equidigital number, since it uses as much as digits as its factorization.

21398557 is an evil number, because the sum of its binary digits is even.

The product of its digits is 75600, while the sum is 40.

The square root of 21398557 is about 4625.8574340332. The cubic root of 21398557 is about 277.6268694561.

The spelling of 21398557 in words is "twenty-one million, three hundred ninety-eight thousand, five hundred fifty-seven".