21668957 has 2 divisors, whose sum is σ = 21668958. Its totient is φ = 21668956.

The previous prime is 21668929. The next prime is 21668963. The reversal of 21668957 is 75986612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 10982596 + 10686361 = 3314^2 + 3269^2 .

It is a cyclic number.

It is not a de Polignac number, because 21668957 - 2¹² = 21664861 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21668917) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10834478 + 10834479.

It is an arithmetic number, because the mean of its divisors is an integer number (10834479).

Almost surely, 2^21668957 is an apocalyptic number.

It is an amenable number.

21668957 is a deficient number, since it is larger than the sum of its proper divisors (1).

21668957 is an equidigital number, since it uses as much as digits as its factorization.

21668957 is an evil number, because the sum of its binary digits is even.

The product of its digits is 181440, while the sum is 44.

The square root of 21668957 is about 4654.9926960200. The cubic root of 21668957 is about 278.7913763511.

The spelling of 21668957 in words is "twenty-one million, six hundred sixty-eight thousand, nine hundred fifty-seven".