231511221 has 24 divisors (see below), whose sum is σ = 342850560. Its totient is φ = 150486336.

The previous prime is 231511201. The next prime is 231511223. The reversal of 231511221 is 122115132.

It is not a de Polignac number, because 231511221 - 2¹⁸ = 231249077 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 231511194 and 231511203.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (231511223) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 65721 + ... + 69153.

It is an arithmetic number, because the mean of its divisors is an integer number (14285440).

Almost surely, 2^231511221 is an apocalyptic number.

It is an amenable number.

231511221 is a deficient number, since it is larger than the sum of its proper divisors (111339339).

231511221 is a wasteful number, since it uses less digits than its factorization.

231511221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3625 (or 3622 counting only the distinct ones).

The product of its digits is 120, while the sum is 18.

The square root of 231511221 is about 15215.4927951743. The cubic root of 231511221 is about 614.0315433649.

Adding to 231511221 its reverse (122115132), we get a palindrome (353626353).

The spelling of 231511221 in words is "two hundred thirty-one million, five hundred eleven thousand, two hundred twenty-one".