644789 has 2 divisors, whose sum is σ = 644790. Its totient is φ = 644788.

The previous prime is 644783. The next prime is 644797. The reversal of 644789 is 987446.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 574564 + 70225 = 758^2 + 265^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-644789 is a prime.

It is an Ulam number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644783) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322394 + 322395.

It is an arithmetic number, because the mean of its divisors is an integer number (322395).

2⁶⁴⁴⁷⁸⁹ is an apocalyptic number.

It is an amenable number.

644789 is a deficient number, since it is larger than the sum of its proper divisors (1).

644789 is an equidigital number, since it uses as much as digits as its factorization.

644789 is an evil number, because the sum of its binary digits is even.

The product of its digits is 48384, while the sum is 38.

The square root of 644789 is about 802.9875466033. The cubic root of 644789 is about 86.3918034205.

The spelling of 644789 in words is "six hundred forty-four thousand, seven hundred eighty-nine".