668540689 has 2 divisors, whose sum is σ = 668540690. Its totient is φ = 668540688.

The previous prime is 668540687. The next prime is 668540723. The reversal of 668540689 is 986045866.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 664608400 + 3932289 = 25780^2 + 1983^2 .

It is a cyclic number.

It is not a de Polignac number, because 668540689 - 2¹ = 668540687 is a prime.

Together with 668540687, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (668540687) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 334270344 + 334270345.

It is an arithmetic number, because the mean of its divisors is an integer number (334270345).

Almost surely, 2^668540689 is an apocalyptic number.

It is an amenable number.

668540689 is a deficient number, since it is larger than the sum of its proper divisors (1).

668540689 is an equidigital number, since it uses as much as digits as its factorization.

668540689 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2488320, while the sum is 52.

The square root of 668540689 is about 25856.1537936330. The cubic root of 668540689 is about 874.3982535875.

It can be divided in two parts, 6685 and 40689, that added together give a palindrome (47374).

The spelling of 668540689 in words is "six hundred sixty-eight million, five hundred forty thousand, six hundred eighty-nine".