644731 has 2 divisors, whose sum is σ = 644732. Its totient is φ = 644730.

The previous prime is 644729. The next prime is 644747. The reversal of 644731 is 137446.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 644731 - 2¹ = 644729 is a prime.

It is a super-2 number, since 2×644731² = 831356124722, which contains 22 as substring.

Together with 644729, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 644696 and 644705.

It is not a weakly prime, because it can be changed into another prime (644701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322365 + 322366.

It is an arithmetic number, because the mean of its divisors is an integer number (322366).

2⁶⁴⁴⁷³¹ is an apocalyptic number.

644731 is a deficient number, since it is larger than the sum of its proper divisors (1).

644731 is an equidigital number, since it uses as much as digits as its factorization.

644731 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2016, while the sum is 25.

The square root of 644731 is about 802.9514306607. The cubic root of 644731 is about 86.3892129737.

The spelling of 644731 in words is "six hundred forty-four thousand, seven hundred thirty-one".