644222221 has 2 divisors, whose sum is σ = 644222222. Its totient is φ = 644222220.

The previous prime is 644222213. The next prime is 644222233. The reversal of 644222221 is 122222446.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 360468196 + 283754025 = 18986^2 + 16845^2 .

It is a cyclic number.

It is not a de Polignac number, because 644222221 - 2³ = 644222213 is a prime.

It is a nialpdrome in base 10.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (644222291) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 322111110 + 322111111.

It is an arithmetic number, because the mean of its divisors is an integer number (322111111).

Almost surely, 2^644222221 is an apocalyptic number.

It is an amenable number.

644222221 is a deficient number, since it is larger than the sum of its proper divisors (1).

644222221 is an equidigital number, since it uses as much as digits as its factorization.

644222221 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3072, while the sum is 25.

The square root of 644222221 is about 25381.5330703250. The cubic root of 644222221 is about 863.6648277871.

Adding to 644222221 its reverse (122222446), we get a palindrome (766444667).

The spelling of 644222221 in words is "six hundred forty-four million, two hundred twenty-two thousand, two hundred twenty-one".