21656959 has 4 divisors (see below), whose sum is σ = 21710320. Its totient is φ = 21603600.

The previous prime is 21656933. The next prime is 21656969. The reversal of 21656959 is 95965612.

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

It is a cyclic number.

It is not a de Polignac number, because 21656959 - 2²¹ = 19559807 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 (21656909) 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, 26067 + ... + 26884.

It is an arithmetic number, because the mean of its divisors is an integer number (5427580).

Almost surely, 2^21656959 is an apocalyptic number.

21656959 is a deficient number, since it is larger than the sum of its proper divisors (53361).

21656959 is an equidigital number, since it uses as much as digits as its factorization.

21656959 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 53360.

The product of its digits is 145800, while the sum is 43.

The square root of 21656959 is about 4653.7037937540. The cubic root of 21656959 is about 278.7399116916.

It can be divided in two parts, 216 and 56959, that added together give a palindrome (57175).

The spelling of 21656959 in words is "twenty-one million, six hundred fifty-six thousand, nine hundred fifty-nine".