666788900021 has 2 divisors, whose sum is σ = 666788900022. Its totient is φ = 666788900020.

The previous prime is 666788899999. The next prime is 666788900059. The reversal of 666788900021 is 120009887666.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 555786651121 + 111002248900 = 745511^2 + 333170^2 .

It is a cyclic number.

It is not a de Polignac number, because 666788900021 - 2³⁰ = 665715158197 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (666788909021) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 333394450010 + 333394450011.

It is an arithmetic number, because the mean of its divisors is an integer number (333394450011).

Almost surely, 2^666788900021 is an apocalyptic number.

It is an amenable number.

666788900021 is a deficient number, since it is larger than the sum of its proper divisors (1).

666788900021 is an equidigital number, since it uses as much as digits as its factorization.

666788900021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1741824, while the sum is 53.

The spelling of 666788900021 in words is "six hundred sixty-six billion, seven hundred eighty-eight million, nine hundred thousand, twenty-one".