665781917 has 2 divisors, whose sum is σ = 665781918. Its totient is φ = 665781916.

The previous prime is 665781899. The next prime is 665781923. The reversal of 665781917 is 719187566.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 647753401 + 18028516 = 25451^2 + 4246^2 .

It is a cyclic number.

It is not a de Polignac number, because 665781917 - 2²² = 661587613 is a prime.

It is a super-2 number, since 2×665781917² = 886531122008389778, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (665781967) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332890958 + 332890959.

It is an arithmetic number, because the mean of its divisors is an integer number (332890959).

Almost surely, 2^665781917 is an apocalyptic number.

It is an amenable number.

665781917 is a deficient number, since it is larger than the sum of its proper divisors (1).

665781917 is an equidigital number, since it uses as much as digits as its factorization.

665781917 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 635040, while the sum is 50.

The square root of 665781917 is about 25802.7501828778. The cubic root of 665781917 is about 873.1938436419.

The spelling of 665781917 in words is "six hundred sixty-five million, seven hundred eighty-one thousand, nine hundred seventeen".