644440217 has 2 divisors, whose sum is σ = 644440218. Its totient is φ = 644440216.

The previous prime is 644440201. The next prime is 644440219. The reversal of 644440217 is 712044446.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 587044441 + 57395776 = 24229^2 + 7576^2 .

It is a cyclic number.

It is not a de Polignac number, because 644440217 - 2⁴ = 644440201 is a prime.

Together with 644440219, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (644440219) 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, 322220108 + 322220109.

It is an arithmetic number, because the mean of its divisors is an integer number (322220109).

Almost surely, 2^644440217 is an apocalyptic number.

It is an amenable number.

644440217 is a deficient number, since it is larger than the sum of its proper divisors (1).

644440217 is an equidigital number, since it uses as much as digits as its factorization.

644440217 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 21504, while the sum is 32.

The square root of 644440217 is about 25385.8270891456. The cubic root of 644440217 is about 863.7622342612.

The spelling of 644440217 in words is "six hundred forty-four million, four hundred forty thousand, two hundred seventeen".