644427191 has 2 divisors, whose sum is σ = 644427192. Its totient is φ = 644427190.

The previous prime is 644427139. The next prime is 644427229. The reversal of 644427191 is 191724446.

It is an a-pointer prime, because the next prime (644427229) can be obtained adding 644427191 to its sum of digits (38).

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 644427191 - 2¹⁸ = 644165047 is a prime.

It is a super-3 number, since 3×644427191³ (a number of 27 digits) contains 333 as substring.

It is equal to p_33518594 and since 644427191 and 33518594 have the same sum of digits, it is a Honaker prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644427131) 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, 322213595 + 322213596.

It is an arithmetic number, because the mean of its divisors is an integer number (322213596).

Almost surely, 2^644427191 is an apocalyptic number.

644427191 is a deficient number, since it is larger than the sum of its proper divisors (1).

644427191 is an equidigital number, since it uses as much as digits as its factorization.

644427191 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 48384, while the sum is 38.

The square root of 644427191 is about 25385.5705273685. The cubic root of 644427191 is about 863.7564145113.

The spelling of 644427191 in words is "six hundred forty-four million, four hundred twenty-seven thousand, one hundred ninety-one".