644021943 has 4 divisors (see below), whose sum is σ = 858695928. Its totient is φ = 429347960.

The previous prime is 644021941. The next prime is 644021951. The reversal of 644021943 is 349120446.

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 644021943 - 2¹ = 644021941 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (644021941) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 107336988 + ... + 107336993.

It is an arithmetic number, because the mean of its divisors is an integer number (214673982).

Almost surely, 2^644021943 is an apocalyptic number.

644021943 is a deficient number, since it is larger than the sum of its proper divisors (214673985).

644021943 is a wasteful number, since it uses less digits than its factorization.

644021943 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 214673984.

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

The square root of 644021943 is about 25377.5874148824. The cubic root of 644021943 is about 863.5753188223.

The spelling of 644021943 in words is "six hundred forty-four million, twenty-one thousand, nine hundred forty-three".