644360665 has 12 divisors (see below), whose sum is σ = 837288684. Its totient is φ = 475834944.

The previous prime is 644360659. The next prime is 644360669. The reversal of 644360665 is 566063446.

It can be written as a sum of positive squares in 6 ways, for example, as 17909824 + 626450841 = 4232^2 + 25029^2 .

It is a de Polignac number, because none of the positive numbers 2^k-644360665 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644360669) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 380434 + ... + 382123.

It is an arithmetic number, because the mean of its divisors is an integer number (69774057).

Almost surely, 2^644360665 is an apocalyptic number.

644360665 is a gapful number since it is divisible by the number (65) formed by its first and last digit.

It is an amenable number.

644360665 is a deficient number, since it is larger than the sum of its proper divisors (192928019).

644360665 is a wasteful number, since it uses less digits than its factorization.

644360665 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 762588 (or 762575 counting only the distinct ones).

The product of its (nonzero) digits is 311040, while the sum is 40.

The square root of 644360665 is about 25384.2601822468. The cubic root of 644360665 is about 863.7266908344.

The spelling of 644360665 in words is "six hundred forty-four million, three hundred sixty thousand, six hundred sixty-five".