644775631 has 2 divisors, whose sum is σ = 644775632. Its totient is φ = 644775630.

The previous prime is 644775613. The next prime is 644775667. The reversal of 644775631 is 136577446.

Together with previous prime (644775613) it forms an Ormiston pair, because they use the same digits, order apart.

It is a weak prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-644775631 is a prime.

It is a super-2 number, since 2×644775631² = 831471228662896322, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644775601) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322387815 + 322387816.

It is an arithmetic number, because the mean of its divisors is an integer number (322387816).

Almost surely, 2^644775631 is an apocalyptic number.

644775631 is a deficient number, since it is larger than the sum of its proper divisors (1).

644775631 is an equidigital number, since it uses as much as digits as its factorization.

644775631 is an evil number, because the sum of its binary digits is even.

The product of its digits is 423360, while the sum is 43.

The square root of 644775631 is about 25392.4325538141. The cubic root of 644775631 is about 863.9120633632.

The spelling of 644775631 in words is "six hundred forty-four million, seven hundred seventy-five thousand, six hundred thirty-one".