21557023 has 2 divisors, whose sum is σ = 21557024. Its totient is φ = 21557022.

The previous prime is 21557017. The next prime is 21557033. The reversal of 21557023 is 32075512.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21557023 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21557033) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10778511 + 10778512.

It is an arithmetic number, because the mean of its divisors is an integer number (10778512).

Almost surely, 2^21557023 is an apocalyptic number.

21557023 is a deficient number, since it is larger than the sum of its proper divisors (1).

21557023 is an equidigital number, since it uses as much as digits as its factorization.

21557023 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2100, while the sum is 25.

The square root of 21557023 is about 4642.9541242618. The cubic root of 21557023 is about 278.3105022288.

The spelling of 21557023 in words is "twenty-one million, five hundred fifty-seven thousand, twenty-three".