665613717995521 has 4 divisors (see below), whose sum is σ = 665831167759444. Its totient is φ = 665396268231600.

The previous prime is 665613717995519. The next prime is 665613717995557. The reversal of 665613717995521 is 125599717316566.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 283846511585025 + 381767206410496 = 16847745^2 + 19538864^2 .

It is a cyclic number.

It is not a de Polignac number, because 665613717995521 - 2¹ = 665613717995519 is a prime.

It is a super-2 number, since 2×665613717995521² (a number of 30 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (665613717995921) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 108724877370 + ... + 108724883491.

It is an arithmetic number, because the mean of its divisors is an integer number (166457791939861).

Almost surely, 2^{665613717995521} is an apocalyptic number.

It is an amenable number.

665613717995521 is a deficient number, since it is larger than the sum of its proper divisors (217449763923).

665613717995521 is a wasteful number, since it uses less digits than its factorization.

665613717995521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 217449763922.

The product of its digits is 642978000, while the sum is 73.

The spelling of 665613717995521 in words is "six hundred sixty-five trillion, six hundred thirteen billion, seven hundred seventeen million, nine hundred ninety-five thousand, five hundred twenty-one".