644741561 has 2 divisors, whose sum is σ = 644741562. Its totient is φ = 644741560.

The previous prime is 644741551. The next prime is 644741567. The reversal of 644741561 is 165147446.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 435765625 + 208975936 = 20875^2 + 14456^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-644741561 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (644741567) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322370780 + 322370781.

It is an arithmetic number, because the mean of its divisors is an integer number (322370781).

Almost surely, 2^644741561 is an apocalyptic number.

It is an amenable number.

644741561 is a deficient number, since it is larger than the sum of its proper divisors (1).

644741561 is an equidigital number, since it uses as much as digits as its factorization.

644741561 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 80640, while the sum is 38.

The square root of 644741561 is about 25391.7616757877. The cubic root of 644741561 is about 863.8968466992.

The spelling of 644741561 in words is "six hundred forty-four million, seven hundred forty-one thousand, five hundred sixty-one".