644464721 has 2 divisors, whose sum is σ = 644464722. Its totient is φ = 644464720.

The previous prime is 644464703. The next prime is 644464727. The reversal of 644464721 is 127464446.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 374848321 + 269616400 = 19361^2 + 16420^2 .

It is a cyclic number.

It is not a de Polignac number, because 644464721 - 2¹⁰ = 644463697 is a prime.

It is a super-2 number, since 2×644464721² = 830669553227215682, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (644464727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322232360 + 322232361.

It is an arithmetic number, because the mean of its divisors is an integer number (322232361).

Almost surely, 2^644464721 is an apocalyptic number.

It is an amenable number.

644464721 is a deficient number, since it is larger than the sum of its proper divisors (1).

644464721 is an equidigital number, since it uses as much as digits as its factorization.

644464721 is an evil number, because the sum of its binary digits is even.

The product of its digits is 129024, while the sum is 38.

The square root of 644464721 is about 25386.3097160655. The cubic root of 644464721 is about 863.7731819338.

The spelling of 644464721 in words is "six hundred forty-four million, four hundred sixty-four thousand, seven hundred twenty-one".