644640013 has 2 divisors, whose sum is σ = 644640014. Its totient is φ = 644640012.

The previous prime is 644639971. The next prime is 644640019. The reversal of 644640013 is 310046446.

It is a happy number.

644640013 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., 643231044 + 1408969 = 25362^2 + 1187^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-644640013 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644640019) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322320006 + 322320007.

It is an arithmetic number, because the mean of its divisors is an integer number (322320007).

Almost surely, 2^644640013 is an apocalyptic number.

It is an amenable number.

644640013 is a deficient number, since it is larger than the sum of its proper divisors (1).

644640013 is an equidigital number, since it uses as much as digits as its factorization.

644640013 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 28.

The square root of 644640013 is about 25389.7619721021. The cubic root of 644640013 is about 863.8514891955.

Adding to 644640013 its reverse (310046446), we get a palindrome (954686459).

The spelling of 644640013 in words is "six hundred forty-four million, six hundred forty thousand, thirteen".