21312857 has 4 divisors (see below), whose sum is σ = 21582720. Its totient is φ = 21042996.

The previous prime is 21312833. The next prime is 21312871. The reversal of 21312857 is 75821312.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21312857 - 2⁶ = 21312793 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21312877) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 134813 + ... + 134970.

It is an arithmetic number, because the mean of its divisors is an integer number (5395680).

Almost surely, 2^21312857 is an apocalyptic number.

It is an amenable number.

21312857 is a deficient number, since it is larger than the sum of its proper divisors (269863).

21312857 is an equidigital number, since it uses as much as digits as its factorization.

21312857 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 269862.

The product of its digits is 3360, while the sum is 29.

The square root of 21312857 is about 4616.5849932607. The cubic root of 21312857 is about 277.2557469816.

The spelling of 21312857 in words is "twenty-one million, three hundred twelve thousand, eight hundred fifty-seven".