644752638161 has 4 divisors (see below), whose sum is σ = 645839911332. Its totient is φ = 643665364992.

The previous prime is 644752638083. The next prime is 644752638227. The reversal of 644752638161 is 161836257446.

It is a happy number.

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 225192007936 + 419560630225 = 474544^2 + 647735^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-644752638161 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (644752628161) 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, 543635696 + ... + 543636881.

It is an arithmetic number, because the mean of its divisors is an integer number (161459977833).

Almost surely, 2^644752638161 is an apocalyptic number.

It is an amenable number.

644752638161 is a deficient number, since it is larger than the sum of its proper divisors (1087273171).

644752638161 is a wasteful number, since it uses less digits than its factorization.

644752638161 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1087273170.

The product of its digits is 5806080, while the sum is 53.

The spelling of 644752638161 in words is "six hundred forty-four billion, seven hundred fifty-two million, six hundred thirty-eight thousand, one hundred sixty-one".