231221561 has 2 divisors, whose sum is σ = 231221562. Its totient is φ = 231221560.

The previous prime is 231221521. The next prime is 231221569. The reversal of 231221561 is 165122132.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 229674025 + 1547536 = 15155^2 + 1244^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-231221561 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (231221569) 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, 115610780 + 115610781.

It is an arithmetic number, because the mean of its divisors is an integer number (115610781).

Almost surely, 2^231221561 is an apocalyptic number.

It is an amenable number.

231221561 is a deficient number, since it is larger than the sum of its proper divisors (1).

231221561 is an equidigital number, since it uses as much as digits as its factorization.

231221561 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 231221561 is about 15205.9712284352. The cubic root of 231221561 is about 613.7753504461.

Adding to 231221561 its reverse (165122132), we get a palindrome (396343693).

The spelling of 231221561 in words is "two hundred thirty-one million, two hundred twenty-one thousand, five hundred sixty-one".