665686686493 has 4 divisors (see below), whose sum is σ = 668161358460. Its totient is φ = 663212014528.

The previous prime is 665686686437. The next prime is 665686686523. The reversal of 665686686493 is 394686686566.

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 405206087364 + 260480599129 = 636558^2 + 510373^2 .

It is a cyclic number.

It is not a de Polignac number, because 665686686493 - 2⁹ = 665686685981 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (665686686893) 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, 1237335580 + ... + 1237336117.

It is an arithmetic number, because the mean of its divisors is an integer number (167040339615).

Almost surely, 2^665686686493 is an apocalyptic number.

It is an amenable number.

665686686493 is a deficient number, since it is larger than the sum of its proper divisors (2474671967).

665686686493 is a wasteful number, since it uses less digits than its factorization.

665686686493 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2474671966.

The product of its digits is 1612431360, while the sum is 73.

Adding to 665686686493 its sum of digits (73), we get a palindrome (665686686566).

The spelling of 665686686493 in words is "six hundred sixty-five billion, six hundred eighty-six million, six hundred eighty-six thousand, four hundred ninety-three".