21611657 has 4 divisors (see below), whose sum is σ = 21623556. Its totient is φ = 21599760.

The previous prime is 21611621. The next prime is 21611669. The reversal of 21611657 is 75611612.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 6056521 + 15555136 = 2461^2 + 3944^2 .

It is a cyclic number.

It is not a de Polignac number, because 21611657 - 2²⁴ = 4834441 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21611617) 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, 2594 + ... + 7067.

It is an arithmetic number, because the mean of its divisors is an integer number (5405889).

Almost surely, 2^21611657 is an apocalyptic number.

It is an amenable number.

21611657 is a deficient number, since it is larger than the sum of its proper divisors (11899).

21611657 is an equidigital number, since it uses as much as digits as its factorization.

21611657 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11898.

The product of its digits is 2520, while the sum is 29.

The square root of 21611657 is about 4648.8339398176. The cubic root of 21611657 is about 278.5454200821.

The spelling of 21611657 in words is "twenty-one million, six hundred eleven thousand, six hundred fifty-seven".