668531135821 has 2 divisors, whose sum is σ = 668531135822. Its totient is φ = 668531135820.

The previous prime is 668531135801. The next prime is 668531135869. The reversal of 668531135821 is 128531135866.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 408416855625 + 260114280196 = 639075^2 + 510014^2 .

It is a cyclic number.

It is not a de Polignac number, because 668531135821 - 2¹⁷ = 668531004749 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (668531135801) 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 as a sum of consecutive naturals, namely, 334265567910 + 334265567911.

It is an arithmetic number, because the mean of its divisors is an integer number (334265567911).

Almost surely, 2^668531135821 is an apocalyptic number.

It is an amenable number.

668531135821 is a deficient number, since it is larger than the sum of its proper divisors (1).

668531135821 is an equidigital number, since it uses as much as digits as its factorization.

668531135821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1036800, while the sum is 49.

The spelling of 668531135821 in words is "six hundred sixty-eight billion, five hundred thirty-one million, one hundred thirty-five thousand, eight hundred twenty-one".