644277661 has 2 divisors, whose sum is σ = 644277662. Its totient is φ = 644277660.

The previous prime is 644277653. The next prime is 644277677. The reversal of 644277661 is 166772446.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 430562500 + 213715161 = 20750^2 + 14619^2 .

It is a cyclic number.

It is not a de Polignac number, because 644277661 - 2³ = 644277653 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644277461) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322138830 + 322138831.

It is an arithmetic number, because the mean of its divisors is an integer number (322138831).

Almost surely, 2^644277661 is an apocalyptic number.

It is an amenable number.

644277661 is a deficient number, since it is larger than the sum of its proper divisors (1).

644277661 is an equidigital number, since it uses as much as digits as its factorization.

644277661 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 338688, while the sum is 43.

The square root of 644277661 is about 25382.6251794412. The cubic root of 644277661 is about 863.6896019530.

The spelling of 644277661 in words is "six hundred forty-four million, two hundred seventy-seven thousand, six hundred sixty-one".