666118777921 has 3 divisors (see below), whose sum is σ = 666119594083. Its totient is φ = 666117961760.

The previous prime is 666118777861. The next prime is 666118777943. The reversal of 666118777921 is 129777811666.

The square root of 666118777921 is 816161.

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

666118777921 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in only one way, i.e., 541933017921 + 124185760000 = 736161^2 + 352400^2 .

It is not a de Polignac number, because 666118777921 - 2²³ = 666110389313 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 666118777921.

It is not an unprimeable number, because it can be changed into a prime (666118777981) by changing a digit.

It is a polite number, since it can be written in 2 ways as a sum of consecutive naturals, for example, 408081 + ... + 1224241.

Almost surely, 2^666118777921 is an apocalyptic number.

666118777921 is the 816161-st square number.

666118777921 is the 408081-st centered octagonal number.

It is an amenable number.

666118777921 is a deficient number, since it is larger than the sum of its proper divisors (816162).

666118777921 is an frugal number, since it uses more digits than its factorization.

666118777921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1632322 (or 816161 counting only the distinct ones).

The product of its digits is 10668672, while the sum is 61.

The spelling of 666118777921 in words is "six hundred sixty-six billion, one hundred eighteen million, seven hundred seventy-seven thousand, nine hundred twenty-one".