21611917 has 2 divisors, whose sum is σ = 21611918. Its totient is φ = 21611916.

The previous prime is 21611897. The next prime is 21611939. The reversal of 21611917 is 71911612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11964681 + 9647236 = 3459^2 + 3106^2 .

It is a cyclic number.

It is not a de Polignac number, because 21611917 - 2¹¹ = 21609869 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21611957) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10805958 + 10805959.

It is an arithmetic number, because the mean of its divisors is an integer number (10805959).

Almost surely, 2^21611917 is an apocalyptic number.

It is an amenable number.

21611917 is a deficient number, since it is larger than the sum of its proper divisors (1).

21611917 is an equidigital number, since it uses as much as digits as its factorization.

21611917 is an evil number, because the sum of its binary digits is even.

The product of its digits is 756, while the sum is 28.

The square root of 21611917 is about 4648.8619037351. The cubic root of 21611917 is about 278.5465370953.

The spelling of 21611917 in words is "twenty-one million, six hundred eleven thousand, nine hundred seventeen".