21957857 has 2 divisors, whose sum is σ = 21957858. Its totient is φ = 21957856.

The previous prime is 21957851. The next prime is 21957877. The reversal of 21957857 is 75875912.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20939776 + 1018081 = 4576^2 + 1009^2 .

It is a cyclic number.

It is not a de Polignac number, because 21957857 - 2⁴ = 21957841 is a prime.

It is not a weakly prime, because it can be changed into another prime (21957851) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10978928 + 10978929.

It is an arithmetic number, because the mean of its divisors is an integer number (10978929).

Almost surely, 2^21957857 is an apocalyptic number.

It is an amenable number.

21957857 is a deficient number, since it is larger than the sum of its proper divisors (1).

21957857 is an equidigital number, since it uses as much as digits as its factorization.

21957857 is an evil number, because the sum of its binary digits is even.

The product of its digits is 176400, while the sum is 44.

The square root of 21957857 is about 4685.9211474373. The cubic root of 21957857 is about 280.0248999965.

The spelling of 21957857 in words is "twenty-one million, nine hundred fifty-seven thousand, eight hundred fifty-seven".