21909857 has 2 divisors, whose sum is σ = 21909858. Its totient is φ = 21909856.

The previous prime is 21909817. The next prime is 21909859. The reversal of 21909857 is 75890912.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 16638241 + 5271616 = 4079^2 + 2296^2 .

It is a cyclic number.

It is not a de Polignac number, because 21909857 - 2¹² = 21905761 is a prime.

Together with 21909859, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (21909859) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10954928 + 10954929.

It is an arithmetic number, because the mean of its divisors is an integer number (10954929).

Almost surely, 2^21909857 is an apocalyptic number.

It is an amenable number.

21909857 is a deficient number, since it is larger than the sum of its proper divisors (1).

21909857 is an equidigital number, since it uses as much as digits as its factorization.

21909857 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 45360, while the sum is 41.

The square root of 21909857 is about 4680.7966202346. The cubic root of 21909857 is about 279.8207057941.

The spelling of 21909857 in words is "twenty-one million, nine hundred nine thousand, eight hundred fifty-seven".