644195609 has 2 divisors, whose sum is σ = 644195610. Its totient is φ = 644195608.

The previous prime is 644195597. The next prime is 644195611. The reversal of 644195609 is 906591446.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 536617225 + 107578384 = 23165^2 + 10372^2 .

It is a cyclic number.

It is not a de Polignac number, because 644195609 - 2⁸ = 644195353 is a prime.

Together with 644195611, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 644195609.

It is not a weakly prime, because it can be changed into another prime (644191609) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322097804 + 322097805.

It is an arithmetic number, because the mean of its divisors is an integer number (322097805).

Almost surely, 2^644195609 is an apocalyptic number.

It is an amenable number.

644195609 is a deficient number, since it is larger than the sum of its proper divisors (1).

644195609 is an equidigital number, since it uses as much as digits as its factorization.

644195609 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 233280, while the sum is 44.

The square root of 644195609 is about 25381.0088254979. The cubic root of 644195609 is about 863.6529353251.

The spelling of 644195609 in words is "six hundred forty-four million, one hundred ninety-five thousand, six hundred nine".