644956391 has 2 divisors, whose sum is σ = 644956392. Its totient is φ = 644956390.

The previous prime is 644956381. The next prime is 644956393. The reversal of 644956391 is 193659446.

It is a happy number.

It is a strong prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-644956391 is a prime.

It is a Sophie Germain prime.

Together with 644956393, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644956393) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322478195 + 322478196.

It is an arithmetic number, because the mean of its divisors is an integer number (322478196).

Almost surely, 2^644956391 is an apocalyptic number.

644956391 is a deficient number, since it is larger than the sum of its proper divisors (1).

644956391 is an equidigital number, since it uses as much as digits as its factorization.

644956391 is an evil number, because the sum of its binary digits is even.

The product of its digits is 699840, while the sum is 47.

The square root of 644956391 is about 25395.9916325392. The cubic root of 644956391 is about 863.9927871304.

The spelling of 644956391 in words is "six hundred forty-four million, nine hundred fifty-six thousand, three hundred ninety-one".