644681717 has 2 divisors, whose sum is σ = 644681718. Its totient is φ = 644681716.

The previous prime is 644681711. The next prime is 644681759. The reversal of 644681717 is 717186446.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 597264721 + 47416996 = 24439^2 + 6886^2 .

It is a cyclic number.

It is not a de Polignac number, because 644681717 - 2⁸ = 644681461 is a prime.

It is a super-2 number, since 2×644681717² = 831229032468136178, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644681711) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322340858 + 322340859.

It is an arithmetic number, because the mean of its divisors is an integer number (322340859).

Almost surely, 2^644681717 is an apocalyptic number.

It is an amenable number.

644681717 is a deficient number, since it is larger than the sum of its proper divisors (1).

644681717 is an equidigital number, since it uses as much as digits as its factorization.

644681717 is an evil number, because the sum of its binary digits is even.

The product of its digits is 225792, while the sum is 44.

The square root of 644681717 is about 25390.5832347349. The cubic root of 644681717 is about 863.8701173109.

The spelling of 644681717 in words is "six hundred forty-four million, six hundred eighty-one thousand, seven hundred seventeen".