644638979 has 2 divisors, whose sum is σ = 644638980. Its totient is φ = 644638978.

The previous prime is 644638949. The next prime is 644638987. The reversal of 644638979 is 979836446.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 644638979 - 2¹⁶ = 644573443 is a prime.

It is not a weakly prime, because it can be changed into another prime (644638909) 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, 322319489 + 322319490.

It is an arithmetic number, because the mean of its divisors is an integer number (322319490).

Almost surely, 2^644638979 is an apocalyptic number.

644638979 is a deficient number, since it is larger than the sum of its proper divisors (1).

644638979 is an equidigital number, since it uses as much as digits as its factorization.

644638979 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 7838208, while the sum is 56.

The square root of 644638979 is about 25389.7416095556. The cubic root of 644638979 is about 863.8510273238.

The spelling of 644638979 in words is "six hundred forty-four million, six hundred thirty-eight thousand, nine hundred seventy-nine".