644381 has 2 divisors, whose sum is σ = 644382. Its totient is φ = 644380.

The previous prime is 644377. The next prime is 644383. The reversal of 644381 is 183446.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 538756 + 105625 = 734^2 + 325^2 .

It is a cyclic number.

It is not a de Polignac number, because 644381 - 2² = 644377 is a prime.

It is a super-2 number, since 2×644381² = 830453746322, which contains 22 as substring.

Together with 644383, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 644381.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644383) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322190 + 322191.

It is an arithmetic number, because the mean of its divisors is an integer number (322191).

2⁶⁴⁴³⁸¹ is an apocalyptic number.

It is an amenable number.

644381 is a deficient number, since it is larger than the sum of its proper divisors (1).

644381 is an equidigital number, since it uses as much as digits as its factorization.

644381 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2304, while the sum is 26.

The square root of 644381 is about 802.7334551394. The cubic root of 644381 is about 86.3735776687.

The spelling of 644381 in words is "six hundred forty-four thousand, three hundred eighty-one".