644896817 has 4 divisors (see below), whose sum is σ = 651282036. Its totient is φ = 638511600.

The previous prime is 644896801. The next prime is 644896859. The reversal of 644896817 is 718698446.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 302794801 + 342102016 = 17401^2 + 18496^2 .

It is a cyclic number.

It is not a de Polignac number, because 644896817 - 2⁴ = 644896801 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644896897) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3192458 + ... + 3192659.

It is an arithmetic number, because the mean of its divisors is an integer number (162820509).

Almost surely, 2^644896817 is an apocalyptic number.

It is an amenable number.

644896817 is a deficient number, since it is larger than the sum of its proper divisors (6385219).

644896817 is a wasteful number, since it uses less digits than its factorization.

644896817 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6385218.

The product of its digits is 2322432, while the sum is 53.

The square root of 644896817 is about 25394.8187038222. The cubic root of 644896817 is about 863.9661842511.

The spelling of 644896817 in words is "six hundred forty-four million, eight hundred ninety-six thousand, eight hundred seventeen".