231561221 has 2 divisors, whose sum is σ = 231561222. Its totient is φ = 231561220.

The previous prime is 231561203. The next prime is 231561229. The reversal of 231561221 is 122165132.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 227104900 + 4456321 = 15070^2 + 2111^2 .

It is a cyclic number.

It is not a de Polignac number, because 231561221 - 2⁶ = 231561157 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (231561229) 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, 115780610 + 115780611.

It is an arithmetic number, because the mean of its divisors is an integer number (115780611).

Almost surely, 2^231561221 is an apocalyptic number.

It is an amenable number.

231561221 is a deficient number, since it is larger than the sum of its proper divisors (1).

231561221 is an equidigital number, since it uses as much as digits as its factorization.

231561221 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 720, while the sum is 23.

The square root of 231561221 is about 15217.1357685998. The cubic root of 231561221 is about 614.0757447749.

It can be divided in two parts, 2315 and 61221, that added together give a palindrome (63536).

The spelling of 231561221 in words is "two hundred thirty-one million, five hundred sixty-one thousand, two hundred twenty-one".