644042391 has 32 divisors (see below), whose sum is σ = 921962496. Its totient is φ = 399168000.

The previous prime is 644042369. The next prime is 644042419. The reversal of 644042391 is 193240446.

It is not a de Polignac number, because 644042391 - 2²² = 639848087 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644042291) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 254211 + ... + 256731.

It is an arithmetic number, because the mean of its divisors is an integer number (28811328).

Almost surely, 2^644042391 is an apocalyptic number.

644042391 is a deficient number, since it is larger than the sum of its proper divisors (277920105).

644042391 is a wasteful number, since it uses less digits than its factorization.

644042391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2663.

The product of its (nonzero) digits is 20736, while the sum is 33.

The square root of 644042391 is about 25377.9902868608. The cubic root of 644042391 is about 863.5844583666.

It can be divided in two parts, 64404 and 2391, that added together give a triangular number (66795 = T₃₆₅).

The spelling of 644042391 in words is "six hundred forty-four million, forty-two thousand, three hundred ninety-one".