21664157 has 4 divisors (see below), whose sum is σ = 21674016. Its totient is φ = 21654300.

The previous prime is 21664147. The next prime is 21664163. The reversal of 21664157 is 75146612.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21664157 - 2⁴ = 21664141 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21664117) 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, 32 + ... + 6582.

It is an arithmetic number, because the mean of its divisors is an integer number (5418504).

Almost surely, 2^21664157 is an apocalyptic number.

It is an amenable number.

21664157 is a deficient number, since it is larger than the sum of its proper divisors (9859).

21664157 is an equidigital number, since it uses as much as digits as its factorization.

21664157 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9858.

The product of its digits is 10080, while the sum is 32.

The square root of 21664157 is about 4654.4770920051. The cubic root of 21664157 is about 278.7707893361.

The spelling of 21664157 in words is "twenty-one million, six hundred sixty-four thousand, one hundred fifty-seven".