231221381 has 2 divisors, whose sum is σ = 231221382. Its totient is φ = 231221380.

The previous prime is 231221299. The next prime is 231221383. The reversal of 231221381 is 183122132.

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., 178890625 + 52330756 = 13375^2 + 7234^2 .

It is a cyclic number.

It is not a de Polignac number, because 231221381 - 2¹⁴ = 231204997 is a prime.

It is a super-2 number, since 2×231221381² = 106926654063094322, which contains 22 as substring.

It is a Sophie Germain prime.

Together with 231221383, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (231221383) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 115610690 + 115610691.

It is an arithmetic number, because the mean of its divisors is an integer number (115610691).

Almost surely, 2^231221381 is an apocalyptic number.

It is an amenable number.

231221381 is a deficient number, since it is larger than the sum of its proper divisors (1).

231221381 is an equidigital number, since it uses as much as digits as its factorization.

231221381 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 576, while the sum is 23.

The square root of 231221381 is about 15205.9653097066. The cubic root of 231221381 is about 613.7751911767.

The spelling of 231221381 in words is "two hundred thirty-one million, two hundred twenty-one thousand, three hundred eighty-one".