644624681 has 2 divisors, whose sum is σ = 644624682. Its totient is φ = 644624680.

The previous prime is 644624677. The next prime is 644624711. The reversal of 644624681 is 186426446.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 446265625 + 198359056 = 21125^2 + 14084^2 .

It is a cyclic number.

It is not a de Polignac number, because 644624681 - 2² = 644624677 is a prime.

It is a super-2 number, since 2×644624681² = 831081958708703522, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (644624641) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322312340 + 322312341.

It is an arithmetic number, because the mean of its divisors is an integer number (322312341).

Almost surely, 2^644624681 is an apocalyptic number.

It is an amenable number.

644624681 is a deficient number, since it is larger than the sum of its proper divisors (1).

644624681 is an equidigital number, since it uses as much as digits as its factorization.

644624681 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 221184, while the sum is 41.

The square root of 644624681 is about 25389.4600375825. The cubic root of 644624681 is about 863.8446405794.

The spelling of 644624681 in words is "six hundred forty-four million, six hundred twenty-four thousand, six hundred eighty-one".