1231511221 has 4 divisors (see below), whose sum is σ = 1240500492. Its totient is φ = 1222521952.

The previous prime is 1231511213. The next prime is 1231511269. The reversal of 1231511221 is 1221151321.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 946239121 + 285272100 = 30761^2 + 16890^2 .

It is a cyclic number.

It is not a de Polignac number, because 1231511221 - 2³ = 1231511213 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (1231511521) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4494430 + ... + 4494703.

It is an arithmetic number, because the mean of its divisors is an integer number (310125123).

Almost surely, 2^1231511221 is an apocalyptic number.

It is an amenable number.

1231511221 is a deficient number, since it is larger than the sum of its proper divisors (8989271).

1231511221 is an equidigital number, since it uses as much as digits as its factorization.

1231511221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8989270.

The product of its digits is 120, while the sum is 19.

The square root of 1231511221 is about 35092.8941667683. The cubic root of 1231511221 is about 1071.8798935039.

Adding to 1231511221 its reverse (1221151321), we get a palindrome (2452662542).

The spelling of 1231511221 in words is "one billion, two hundred thirty-one million, five hundred eleven thousand, two hundred twenty-one".