644811901 has 2 divisors, whose sum is σ = 644811902. Its totient is φ = 644811900.

The previous prime is 644811857. The next prime is 644811917. The reversal of 644811901 is 109118446.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 588111001 + 56700900 = 24251^2 + 7530^2 .

It is a cyclic number.

It is not a de Polignac number, because 644811901 - 2⁹ = 644811389 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644811971) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322405950 + 322405951.

It is an arithmetic number, because the mean of its divisors is an integer number (322405951).

Almost surely, 2^644811901 is an apocalyptic number.

It is an amenable number.

644811901 is a deficient number, since it is larger than the sum of its proper divisors (1).

644811901 is an equidigital number, since it uses as much as digits as its factorization.

644811901 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 6912, while the sum is 34.

The square root of 644811901 is about 25393.1467329278. The cubic root of 644811901 is about 863.9282620229.

The spelling of 644811901 in words is "six hundred forty-four million, eight hundred eleven thousand, nine hundred one".