644011721 has 2 divisors, whose sum is σ = 644011722. Its totient is φ = 644011720.

The previous prime is 644011681. The next prime is 644011733. The reversal of 644011721 is 127110446.

644011721 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., 337236496 + 306775225 = 18364^2 + 17515^2 .

It is a cyclic number.

It is not a de Polignac number, because 644011721 - 2⁶ = 644011657 is a prime.

It is not a weakly prime, because it can be changed into another prime (644010721) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322005860 + 322005861.

It is an arithmetic number, because the mean of its divisors is an integer number (322005861).

Almost surely, 2^644011721 is an apocalyptic number.

It is an amenable number.

644011721 is a deficient number, since it is larger than the sum of its proper divisors (1).

644011721 is an equidigital number, since it uses as much as digits as its factorization.

644011721 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1344, while the sum is 26.

The square root of 644011721 is about 25377.3860159001. The cubic root of 644011721 is about 863.5707498716.

The spelling of 644011721 in words is "six hundred forty-four million, eleven thousand, seven hundred twenty-one".