665787516661 has 4 divisors (see below), whose sum is σ = 665983975500. Its totient is φ = 665591057824.

The previous prime is 665787516643. The next prime is 665787516671. The reversal of 665787516661 is 166615787566.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 166615787566 = 2 ⋅83307893783.

It can be written as a sum of positive squares in 2 ways, for example, as 460301187025 + 205486329636 = 678455^2 + 453306^2 .

It is a cyclic number.

It is not a de Polignac number, because 665787516661 - 2⁵ = 665787516629 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 665787516593 and 665787516602.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (665787516601) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 98224336 + ... + 98231113.

It is an arithmetic number, because the mean of its divisors is an integer number (166495993875).

Almost surely, 2^665787516661 is an apocalyptic number.

It is an amenable number.

665787516661 is a deficient number, since it is larger than the sum of its proper divisors (196458839).

665787516661 is a wasteful number, since it uses less digits than its factorization.

665787516661 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 196458838.

The product of its digits is 76204800, while the sum is 64.

The spelling of 665787516661 in words is "six hundred sixty-five billion, seven hundred eighty-seven million, five hundred sixteen thousand, six hundred sixty-one".