668236781 has 2 divisors, whose sum is σ = 668236782. Its totient is φ = 668236780.

The previous prime is 668236771. The next prime is 668236823. The reversal of 668236781 is 187632866.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 496888681 + 171348100 = 22291^2 + 13090^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-668236781 is a prime.

It is a super-2 number, since 2×668236781² = 893080790962483922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (668236711) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 334118390 + 334118391.

It is an arithmetic number, because the mean of its divisors is an integer number (334118391).

Almost surely, 2^668236781 is an apocalyptic number.

It is an amenable number.

668236781 is a deficient number, since it is larger than the sum of its proper divisors (1).

668236781 is an equidigital number, since it uses as much as digits as its factorization.

668236781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 580608, while the sum is 47.

The square root of 668236781 is about 25850.2762267640. The cubic root of 668236781 is about 874.2657376436.

The spelling of 668236781 in words is "six hundred sixty-eight million, two hundred thirty-six thousand, seven hundred eighty-one".