644039581 has 2 divisors, whose sum is σ = 644039582. Its totient is φ = 644039580.

The previous prime is 644039567. The next prime is 644039587. The reversal of 644039581 is 185930446.

644039581 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 612117081 + 31922500 = 24741^2 + 5650^2 .

It is a cyclic number.

It is not a de Polignac number, because 644039581 - 2¹³ = 644031389 is a prime.

It is a super-2 number, since 2×644039581² = 829573963789311122, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644039587) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322019790 + 322019791.

It is an arithmetic number, because the mean of its divisors is an integer number (322019791).

Almost surely, 2^644039581 is an apocalyptic number.

It is an amenable number.

644039581 is a deficient number, since it is larger than the sum of its proper divisors (1).

644039581 is an equidigital number, since it uses as much as digits as its factorization.

644039581 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 103680, while the sum is 40.

The square root of 644039581 is about 25377.9349238664. The cubic root of 644039581 is about 863.5832024059.

It can be divided in two parts, 64403 and 9581, that added together give a square (73984 = 272²).

The spelling of 644039581 in words is "six hundred forty-four million, thirty-nine thousand, five hundred eighty-one".