668638196209 has 9 divisors (see below), whose sum is σ = 705698261067. Its totient is φ = 633431993544.

The previous prime is 668638196203. The next prime is 668638196269. The reversal of 668638196209 is 902691836866.

The square root of 668638196209 is 817703.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in only one way, i.e., 6973085025 + 661665111184 = 83505^2 + 813428^2 .

It is not a de Polignac number, because 668638196209 - 2²⁷ = 668503978481 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (668638196203) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 15514839 + ... + 15557875.

Almost surely, 2^668638196209 is an apocalyptic number.

668638196209 is the 817703-rd square number.

668638196209 is the 408852-nd centered octagonal number.

It is an amenable number.

668638196209 is a deficient number, since it is larger than the sum of its proper divisors (37060064858).

668638196209 is an frugal number, since it uses more digits than its factorization.

668638196209 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 86112 (or 43056 counting only the distinct ones).

The product of its (nonzero) digits is 40310784, while the sum is 64.

Multiplying 668638196209 by its sum of digits (64), we get a square (42792844557376 = 6541624²).

The spelling of 668638196209 in words is "six hundred sixty-eight billion, six hundred thirty-eight million, one hundred ninety-six thousand, two hundred nine".