21356657 has 4 divisors (see below), whose sum is σ = 24407616. Its totient is φ = 18305700.

The previous prime is 21356653. The next prime is 21356689. The reversal of 21356657 is 75665312.

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 not a de Polignac number, because 21356657 - 2² = 21356653 is a prime.

It is a super-2 number, since 2×21356657² = 912213596431298, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21356653) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1525469 + ... + 1525482.

It is an arithmetic number, because the mean of its divisors is an integer number (6101904).

Almost surely, 2^21356657 is an apocalyptic number.

It is an amenable number.

21356657 is a deficient number, since it is larger than the sum of its proper divisors (3050959).

21356657 is an equidigital number, since it uses as much as digits as its factorization.

21356657 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3050958.

The product of its digits is 37800, while the sum is 35.

The square root of 21356657 is about 4621.3263247687. The cubic root of 21356657 is about 277.4455462235.

The spelling of 21356657 in words is "twenty-one million, three hundred fifty-six thousand, six hundred fifty-seven".