21557057 has 2 divisors, whose sum is σ = 21557058. Its totient is φ = 21557056.

The previous prime is 21557047. The next prime is 21557099. The reversal of 21557057 is 75075512.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 19571776 + 1985281 = 4424^2 + 1409^2 .

It is a cyclic number.

It is not a de Polignac number, because 21557057 - 2¹⁸ = 21294913 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21557017) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10778528 + 10778529.

It is an arithmetic number, because the mean of its divisors is an integer number (10778529).

Almost surely, 2^21557057 is an apocalyptic number.

It is an amenable number.

21557057 is a deficient number, since it is larger than the sum of its proper divisors (1).

21557057 is an equidigital number, since it uses as much as digits as its factorization.

21557057 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 12250, while the sum is 32.

The square root of 21557057 is about 4642.9577857224. The cubic root of 21557057 is about 278.3106485470.

The spelling of 21557057 in words is "twenty-one million, five hundred fifty-seven thousand, fifty-seven".