21608957 has 2 divisors, whose sum is σ = 21608958. Its totient is φ = 21608956.

The previous prime is 21608941. The next prime is 21608959. The reversal of 21608957 is 75980612.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20666116 + 942841 = 4546^2 + 971^2 .

It is a cyclic number.

It is not a de Polignac number, because 21608957 - 2⁴ = 21608941 is a prime.

Together with 21608959, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21608957.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21608959) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10804478 + 10804479.

It is an arithmetic number, because the mean of its divisors is an integer number (10804479).

Almost surely, 2^21608957 is an apocalyptic number.

It is an amenable number.

21608957 is a deficient number, since it is larger than the sum of its proper divisors (1).

21608957 is an equidigital number, since it uses as much as digits as its factorization.

21608957 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 30240, while the sum is 38.

The square root of 21608957 is about 4648.5435353452. The cubic root of 21608957 is about 278.5338197999.

The spelling of 21608957 in words is "twenty-one million, six hundred eight thousand, nine hundred fifty-seven".