644221969 has 2 divisors, whose sum is σ = 644221970. Its totient is φ = 644221968.

The previous prime is 644221909. The next prime is 644221993. The reversal of 644221969 is 969122446.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 349241344 + 294980625 = 18688^2 + 17175^2 .

It is a cyclic number.

It is not a de Polignac number, because 644221969 - 2²⁷ = 510004241 is a prime.

It is a super-2 number, since 2×644221969² = 830043890684473922, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (644221909) 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, 322110984 + 322110985.

It is an arithmetic number, because the mean of its divisors is an integer number (322110985).

Almost surely, 2^644221969 is an apocalyptic number.

It is an amenable number.

644221969 is a deficient number, since it is larger than the sum of its proper divisors (1).

644221969 is an equidigital number, since it uses as much as digits as its factorization.

644221969 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 186624, while the sum is 43.

The square root of 644221969 is about 25381.5281060853. The cubic root of 644221969 is about 863.6647151740.

The spelling of 644221969 in words is "six hundred forty-four million, two hundred twenty-one thousand, nine hundred sixty-nine".