644721943 has 2 divisors, whose sum is σ = 644721944. Its totient is φ = 644721942.

The previous prime is 644721941. The next prime is 644722019. The reversal of 644721943 is 349127446.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 644721943 - 2¹ = 644721941 is a prime.

Together with 644721941, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 644721896 and 644721905.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644721941) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322360971 + 322360972.

It is an arithmetic number, because the mean of its divisors is an integer number (322360972).

Almost surely, 2^644721943 is an apocalyptic number.

644721943 is a deficient number, since it is larger than the sum of its proper divisors (1).

644721943 is an equidigital number, since it uses as much as digits as its factorization.

644721943 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 145152, while the sum is 40.

The square root of 644721943 is about 25391.3753664507. The cubic root of 644721943 is about 863.8880844802. Note that the first 3 decimals are identical.

The spelling of 644721943 in words is "six hundred forty-four million, seven hundred twenty-one thousand, nine hundred forty-three".