668991613 has 4 divisors (see below), whose sum is σ = 670276188. Its totient is φ = 667707040.

The previous prime is 668991611. The next prime is 668991623. The reversal of 668991613 is 316199866.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 316199866 = 2 ⋅158099933.

It can be written as a sum of positive squares in 2 ways, for example, as 451222564 + 217769049 = 21242^2 + 14757^2 .

It is a cyclic number.

It is not a de Polignac number, because 668991613 - 2¹ = 668991611 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 (668991611) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 641506 + ... + 642547.

It is an arithmetic number, because the mean of its divisors is an integer number (167569047).

Almost surely, 2^668991613 is an apocalyptic number.

It is an amenable number.

668991613 is a deficient number, since it is larger than the sum of its proper divisors (1284575).

668991613 is a wasteful number, since it uses less digits than its factorization.

668991613 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1284574.

The product of its digits is 419904, while the sum is 49.

The square root of 668991613 is about 25864.8721821702. The cubic root of 668991613 is about 874.5948003598.

The spelling of 668991613 in words is "six hundred sixty-eight million, nine hundred ninety-one thousand, six hundred thirteen".