644956789 has 4 divisors (see below), whose sum is σ = 655888320. Its totient is φ = 634025260.

The previous prime is 644956759. The next prime is 644956813. The reversal of 644956789 is 987659446.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 987659446 = 2 ⋅493829723.

It is a cyclic number.

It is not a de Polignac number, because 644956789 - 2¹¹ = 644954741 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644956759) 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, 5465677 + ... + 5465794.

It is an arithmetic number, because the mean of its divisors is an integer number (163972080).

Almost surely, 2^644956789 is an apocalyptic number.

It is an amenable number.

644956789 is a deficient number, since it is larger than the sum of its proper divisors (10931531).

644956789 is a wasteful number, since it uses less digits than its factorization.

644956789 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10931530.

The product of its digits is 13063680, while the sum is 58.

The square root of 644956789 is about 25395.9994684202. Note that the first 3 decimals coincide. The cubic root of 644956789 is about 863.9929648526.

The spelling of 644956789 in words is "six hundred forty-four million, nine hundred fifty-six thousand, seven hundred eighty-nine".