231309521 has 2 divisors, whose sum is σ = 231309522. Its totient is φ = 231309520.

The previous prime is 231309473. The next prime is 231309523. The reversal of 231309521 is 125903132.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 121793296 + 109516225 = 11036^2 + 10465^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-231309521 is a prime.

It is a Sophie Germain prime.

Together with 231309523, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (231309523) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 115654760 + 115654761.

It is an arithmetic number, because the mean of its divisors is an integer number (115654761).

Almost surely, 2^231309521 is an apocalyptic number.

It is an amenable number.

231309521 is a deficient number, since it is larger than the sum of its proper divisors (1).

231309521 is an equidigital number, since it uses as much as digits as its factorization.

231309521 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1620, while the sum is 26.

The square root of 231309521 is about 15208.8632382568. The cubic root of 231309521 is about 613.8531702295.

The spelling of 231309521 in words is "two hundred thirty-one million, three hundred nine thousand, five hundred twenty-one".