668555861 has 2 divisors, whose sum is σ = 668555862. Its totient is φ = 668555860.

The previous prime is 668555857. The next prime is 668555863. The reversal of 668555861 is 168555866.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 471714961 + 196840900 = 21719^2 + 14030^2 .

It is a cyclic number.

It is not a de Polignac number, because 668555861 - 2² = 668555857 is a prime.

It is a Sophie Germain prime.

Together with 668555863, it forms a pair of twin primes.

It is a Chen 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 (668555863) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 334277930 + 334277931.

It is an arithmetic number, because the mean of its divisors is an integer number (334277931).

Almost surely, 2^668555861 is an apocalyptic number.

It is an amenable number.

668555861 is a deficient number, since it is larger than the sum of its proper divisors (1).

668555861 is an equidigital number, since it uses as much as digits as its factorization.

668555861 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1728000, while the sum is 50.

The square root of 668555861 is about 25856.4471844064. The cubic root of 668555861 is about 874.4048681287.

The spelling of 668555861 in words is "six hundred sixty-eight million, five hundred fifty-five thousand, eight hundred sixty-one".