644863859 has 2 divisors, whose sum is σ = 644863860. Its totient is φ = 644863858.

The previous prime is 644863783. The next prime is 644863871. The reversal of 644863859 is 958368446.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 644863859 - 2²⁴ = 628086643 is a prime.

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 644863859.

It is not a weakly prime, because it can be changed into another prime (644868859) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322431929 + 322431930.

It is an arithmetic number, because the mean of its divisors is an integer number (322431930).

Almost surely, 2^644863859 is an apocalyptic number.

644863859 is a deficient number, since it is larger than the sum of its proper divisors (1).

644863859 is an equidigital number, since it uses as much as digits as its factorization.

644863859 is an evil number, because the sum of its binary digits is even.

The product of its digits is 4976640, while the sum is 53.

The square root of 644863859 is about 25394.1697836334. The cubic root of 644863859 is about 863.9514660916.

It can be divided in two parts, 6448 and 63859, that added together give a palindrome (70307).

The spelling of 644863859 in words is "six hundred forty-four million, eight hundred sixty-three thousand, eight hundred fifty-nine".