644720641 has 2 divisors, whose sum is σ = 644720642. Its totient is φ = 644720640.

The previous prime is 644720603. The next prime is 644720647. The reversal of 644720641 is 146027446.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 506070016 + 138650625 = 22496^2 + 11775^2 .

It is a cyclic number.

It is not a de Polignac number, because 644720641 - 2⁷ = 644720513 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 644720597 and 644720606.

It is not a weakly prime, because it can be changed into another prime (644720647) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322360320 + 322360321.

It is an arithmetic number, because the mean of its divisors is an integer number (322360321).

Almost surely, 2^644720641 is an apocalyptic number.

It is an amenable number.

644720641 is a deficient number, since it is larger than the sum of its proper divisors (1).

644720641 is an equidigital number, since it uses as much as digits as its factorization.

644720641 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 32256, while the sum is 34.

The square root of 644720641 is about 25391.3497278108. The cubic root of 644720641 is about 863.8875029463.

The spelling of 644720641 in words is "six hundred forty-four million, seven hundred twenty thousand, six hundred forty-one".