231521021 has 2 divisors, whose sum is σ = 231521022. Its totient is φ = 231521020.

The previous prime is 231521009. The next prime is 231521027. The reversal of 231521021 is 120125132.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 231465796 + 55225 = 15214^2 + 235^2 .

It is a cyclic number.

It is not a de Polignac number, because 231521021 - 2⁶ = 231520957 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (231521027) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 115760510 + 115760511.

It is an arithmetic number, because the mean of its divisors is an integer number (115760511).

Almost surely, 2^231521021 is an apocalyptic number.

It is an amenable number.

231521021 is a deficient number, since it is larger than the sum of its proper divisors (1).

231521021 is an equidigital number, since it uses as much as digits as its factorization.

231521021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 120, while the sum is 17.

The square root of 231521021 is about 15215.8148319438. The cubic root of 231521021 is about 614.0402073427.

Adding to 231521021 its reverse (120125132), we get a palindrome (351646153).

The spelling of 231521021 in words is "two hundred thirty-one million, five hundred twenty-one thousand, twenty-one".