644643871617 has 16 divisors (see below), whose sum is σ = 883203289920. Its totient is φ = 417935299392.

The previous prime is 644643871607. The next prime is 644643871621. The reversal of 644643871617 is 716178346446.

It is a happy number.

It is not a de Polignac number, because 644643871617 - 2¹⁵ = 644643838849 is a prime.

It is not an unprimeable number, because it can be changed into a prime (644643871607) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1252767 + ... + 1690772.

It is an arithmetic number, because the mean of its divisors is an integer number (55200205620).

Almost surely, 2^644643871617 is an apocalyptic number.

It is an amenable number.

644643871617 is a deficient number, since it is larger than the sum of its proper divisors (238559418303).

644643871617 is a wasteful number, since it uses less digits than its factorization.

644643871617 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2945552.

The product of its digits is 16257024, while the sum is 57.

The spelling of 644643871617 in words is "six hundred forty-four billion, six hundred forty-three million, eight hundred seventy-one thousand, six hundred seventeen".