21180917 has 2 divisors, whose sum is σ = 21180918. Its totient is φ = 21180916.

The previous prime is 21180893. The next prime is 21180923. The reversal of 21180917 is 71908112.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20016676 + 1164241 = 4474^2 + 1079^2 .

It is a cyclic number.

It is not a de Polignac number, because 21180917 - 2²⁰ = 20132341 is a prime.

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 21180917.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21180947) 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, 10590458 + 10590459.

It is an arithmetic number, because the mean of its divisors is an integer number (10590459).

Almost surely, 2^21180917 is an apocalyptic number.

It is an amenable number.

21180917 is a deficient number, since it is larger than the sum of its proper divisors (1).

21180917 is an equidigital number, since it uses as much as digits as its factorization.

21180917 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1008, while the sum is 29.

The square root of 21180917 is about 4602.2730253647. The cubic root of 21180917 is about 276.6824330945.

The spelling of 21180917 in words is "twenty-one million, one hundred eighty thousand, nine hundred seventeen".