636221221 has 2 divisors, whose sum is σ = 636221222. Its totient is φ = 636221220.

The previous prime is 636221197. The next prime is 636221237. The reversal of 636221221 is 122122636.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 320768100 + 315453121 = 17910^2 + 17761^2 .

It is a cyclic number.

It is not a de Polignac number, because 636221221 - 2⁹ = 636220709 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (636221021) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 318110610 + 318110611.

It is an arithmetic number, because the mean of its divisors is an integer number (318110611).

Almost surely, 2^636221221 is an apocalyptic number.

It is an amenable number.

636221221 is a deficient number, since it is larger than the sum of its proper divisors (1).

636221221 is an equidigital number, since it uses as much as digits as its factorization.

636221221 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1728, while the sum is 25.

The square root of 636221221 is about 25223.4260361276. The cubic root of 636221221 is about 860.0744576781.

Adding to 636221221 its reverse (122122636), we get a palindrome (758343857).

The spelling of 636221221 in words is "six hundred thirty-six million, two hundred twenty-one thousand, two hundred twenty-one".