21715857 has 20 divisors (see below), whose sum is σ = 32710656. Its totient is φ = 14356440.

The previous prime is 21715853. The next prime is 21715861. The reversal of 21715857 is 75851712.

21715857 is a `hidden beast` number, since 2 + 1 + 71 + 585 + 7 = 666.

It is an interprime number because it is at equal distance from previous prime (21715853) and next prime (21715861).

It is not a de Polignac number, because 21715857 - 2² = 21715853 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21715853) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 9232 + ... + 11342.

Almost surely, 2^21715857 is an apocalyptic number.

21715857 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

It is an amenable number.

21715857 is a deficient number, since it is larger than the sum of its proper divisors (10994799).

21715857 is a wasteful number, since it uses less digits than its factorization.

21715857 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2250 (or 2241 counting only the distinct ones).

The product of its digits is 19600, while the sum is 36.

The square root of 21715857 is about 4660.0275750257. The cubic root of 21715857 is about 278.9923688513.

The spelling of 21715857 in words is "twenty-one million, seven hundred fifteen thousand, eight hundred fifty-seven".