21656857 has 2 divisors, whose sum is σ = 21656858. Its totient is φ = 21656856.

The previous prime is 21656849. The next prime is 21656863. The reversal of 21656857 is 75865612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20466576 + 1190281 = 4524^2 + 1091^2 .

It is a cyclic number.

It is not a de Polignac number, because 21656857 - 2³ = 21656849 is a prime.

It is not a weakly prime, because it can be changed into another prime (21656867) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10828428 + 10828429.

It is an arithmetic number, because the mean of its divisors is an integer number (10828429).

Almost surely, 2^21656857 is an apocalyptic number.

It is an amenable number.

21656857 is a deficient number, since it is larger than the sum of its proper divisors (1).

21656857 is an equidigital number, since it uses as much as digits as its factorization.

21656857 is an evil number, because the sum of its binary digits is even.

The product of its digits is 100800, while the sum is 40.

The square root of 21656857 is about 4653.6928347281. The cubic root of 21656857 is about 278.7394740876.

The spelling of 21656857 in words is "twenty-one million, six hundred fifty-six thousand, eight hundred fifty-seven".