644221901 has 2 divisors, whose sum is σ = 644221902. Its totient is φ = 644221900.

The previous prime is 644221873. The next prime is 644221909. The reversal of 644221901 is 109122446.

644221901 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 392238025 + 251983876 = 19805^2 + 15874^2 .

It is a cyclic number.

It is not a de Polignac number, because 644221901 - 2¹⁴ = 644205517 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644221909) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322110950 + 322110951.

It is an arithmetic number, because the mean of its divisors is an integer number (322110951).

Almost surely, 2^644221901 is an apocalyptic number.

It is an amenable number.

644221901 is a deficient number, since it is larger than the sum of its proper divisors (1).

644221901 is an equidigital number, since it uses as much as digits as its factorization.

644221901 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 3456, while the sum is 29.

The square root of 644221901 is about 25381.5267665284. The cubic root of 644221901 is about 863.6646847864.

The spelling of 644221901 in words is "six hundred forty-four million, two hundred twenty-one thousand, nine hundred one".