21656413 has 4 divisors (see below), whose sum is σ = 21667680. Its totient is φ = 21645148.

The previous prime is 21656377. The next prime is 21656429. The reversal of 21656413 is 31465612.

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 21656413 - 2⁹ = 21655901 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 (21656513) 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, 1945 + ... + 6862.

It is an arithmetic number, because the mean of its divisors is an integer number (5416920).

Almost surely, 2^21656413 is an apocalyptic number.

It is an amenable number.

21656413 is a deficient number, since it is larger than the sum of its proper divisors (11267).

21656413 is an equidigital number, since it uses as much as digits as its factorization.

21656413 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11266.

The product of its digits is 4320, while the sum is 28.

The square root of 21656413 is about 4653.6451304327. The cubic root of 21656413 is about 278.7375692071.

The spelling of 21656413 in words is "twenty-one million, six hundred fifty-six thousand, four hundred thirteen".