21995917 has 2 divisors, whose sum is σ = 21995918. Its totient is φ = 21995916.

The previous prime is 21995903. The next prime is 21995921. The reversal of 21995917 is 71959912.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19236996 + 2758921 = 4386^2 + 1661^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21995917 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21996917) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10997958 + 10997959.

It is an arithmetic number, because the mean of its divisors is an integer number (10997959).

Almost surely, 2^21995917 is an apocalyptic number.

It is an amenable number.

21995917 is a deficient number, since it is larger than the sum of its proper divisors (1).

21995917 is an equidigital number, since it uses as much as digits as its factorization.

21995917 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 51030, while the sum is 43.

The square root of 21995917 is about 4689.9804903645. The cubic root of 21995917 is about 280.1865975588.

The spelling of 21995917 in words is "twenty-one million, nine hundred ninety-five thousand, nine hundred seventeen".