665716873621 has 2 divisors, whose sum is σ = 665716873622. Its totient is φ = 665716873620.

The previous prime is 665716873537. The next prime is 665716873643. The reversal of 665716873621 is 126378617566.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 509351988721 + 156364884900 = 713689^2 + 395430^2 .

It is a cyclic number.

It is not a de Polignac number, because 665716873621 - 2²⁷ = 665582655893 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (665716873421) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332858436810 + 332858436811.

It is an arithmetic number, because the mean of its divisors is an integer number (332858436811).

Almost surely, 2^665716873621 is an apocalyptic number.

It is an amenable number.

665716873621 is a deficient number, since it is larger than the sum of its proper divisors (1).

665716873621 is an equidigital number, since it uses as much as digits as its factorization.

665716873621 is an evil number, because the sum of its binary digits is even.

The product of its digits is 15240960, while the sum is 58.

The spelling of 665716873621 in words is "six hundred sixty-five billion, seven hundred sixteen million, eight hundred seventy-three thousand, six hundred twenty-one".