21656911 has 2 divisors, whose sum is σ = 21656912. Its totient is φ = 21656910.

The previous prime is 21656909. The next prime is 21656923. The reversal of 21656911 is 11965612.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 21656911 - 2¹ = 21656909 is a prime.

Together with 21656909, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21656311) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10828455 + 10828456.

It is an arithmetic number, because the mean of its divisors is an integer number (10828456).

Almost surely, 2^21656911 is an apocalyptic number.

21656911 is a deficient number, since it is larger than the sum of its proper divisors (1).

21656911 is an equidigital number, since it uses as much as digits as its factorization.

21656911 is an evil number, because the sum of its binary digits is even.

The product of its digits is 3240, while the sum is 31.

The square root of 21656911 is about 4653.6986365686. The cubic root of 21656911 is about 278.7397057605.

The spelling of 21656911 in words is "twenty-one million, six hundred fifty-six thousand, nine hundred eleven".