644880791 has 4 divisors (see below), whose sum is σ = 649209000. Its totient is φ = 640552584.

The previous prime is 644880787. The next prime is 644880799. The reversal of 644880791 is 197088446.

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

It is a cyclic number.

It is not a de Polignac number, because 644880791 - 2² = 644880787 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 (644880799) 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, 2163881 + ... + 2164178.

It is an arithmetic number, because the mean of its divisors is an integer number (162302250).

Almost surely, 2^644880791 is an apocalyptic number.

644880791 is a deficient number, since it is larger than the sum of its proper divisors (4328209).

644880791 is a wasteful number, since it uses less digits than its factorization.

644880791 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4328208.

The product of its (nonzero) digits is 387072, while the sum is 47.

The square root of 644880791 is about 25394.5031650552. The cubic root of 644880791 is about 863.9590275316.

The spelling of 644880791 in words is "six hundred forty-four million, eight hundred eighty thousand, seven hundred ninety-one".