644956637 has 4 divisors (see below), whose sum is σ = 694568700. Its totient is φ = 595344576.

The previous prime is 644956619. The next prime is 644956667. The reversal of 644956637 is 736659446.

644956637 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 736659446 = 2 ⋅368329723.

It can be written as a sum of positive squares in 2 ways, for example, as 336392281 + 308564356 = 18341^2 + 17566^2 .

It is a cyclic number.

It is not a de Polignac number, because 644956637 - 2⁸ = 644956381 is a prime.

It is a super-2 number, since 2×644956637² = 831938127220699538, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644956667) 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, 24806012 + ... + 24806037.

It is an arithmetic number, because the mean of its divisors is an integer number (173642175).

Almost surely, 2^644956637 is an apocalyptic number.

It is an amenable number.

644956637 is a deficient number, since it is larger than the sum of its proper divisors (49612063).

644956637 is a wasteful number, since it uses less digits than its factorization.

644956637 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 49612062.

The product of its digits is 3265920, while the sum is 50.

The square root of 644956637 is about 25395.9964758227. The cubic root of 644956637 is about 863.9928969788.

The spelling of 644956637 in words is "six hundred forty-four million, nine hundred fifty-six thousand, six hundred thirty-seven".