668913681221 has 2 divisors, whose sum is σ = 668913681222. Its totient is φ = 668913681220.

The previous prime is 668913681127. The next prime is 668913681223. The reversal of 668913681221 is 122186319866.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 660255378721 + 8658302500 = 812561^2 + 93050^2 .

It is a cyclic number.

It is not a de Polignac number, because 668913681221 - 2³⁰ = 667839939397 is a prime.

Together with 668913681223, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (668913681223) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 334456840610 + 334456840611.

It is an arithmetic number, because the mean of its divisors is an integer number (334456840611).

Almost surely, 2^668913681221 is an apocalyptic number.

It is an amenable number.

668913681221 is a deficient number, since it is larger than the sum of its proper divisors (1).

668913681221 is an equidigital number, since it uses as much as digits as its factorization.

668913681221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1492992, while the sum is 53.

The spelling of 668913681221 in words is "six hundred sixty-eight billion, nine hundred thirteen million, six hundred eighty-one thousand, two hundred twenty-one".