21451657 has 4 divisors (see below), whose sum is σ = 21466180. Its totient is φ = 21437136.

The previous prime is 21451649. The next prime is 21451669. The reversal of 21451657 is 75615412.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 8231161 + 13220496 = 2869^2 + 3636^2 .

It is a cyclic number.

It is not a de Polignac number, because 21451657 - 2³ = 21451649 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21451607) 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, 4758 + ... + 8095.

It is an arithmetic number, because the mean of its divisors is an integer number (5366545).

Almost surely, 2^21451657 is an apocalyptic number.

It is an amenable number.

21451657 is a deficient number, since it is larger than the sum of its proper divisors (14523).

21451657 is a wasteful number, since it uses less digits than its factorization.

21451657 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14522.

The product of its digits is 8400, while the sum is 31.

The square root of 21451657 is about 4631.5933543436. The cubic root of 21451657 is about 277.8563212144.

The spelling of 21451657 in words is "twenty-one million, four hundred fifty-one thousand, six hundred fifty-seven".