999991231 has 2 divisors, whose sum is σ = 999991232. Its totient is φ = 999991230.

The previous prime is 999991229. The next prime is 999991241. The reversal of 999991231 is 132199999.

It is a weak prime.

It is an emirp because it is prime and its reverse (132199999) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 999991231 - 2¹ = 999991229 is a prime.

It is a super-2 number, since 2×999991231² = 1999964924153790722, which contains 22 as substring.

Together with 999991229, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (999991241) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 499995615 + 499995616.

It is an arithmetic number, because the mean of its divisors is an integer number (499995616).

Almost surely, 2^999991231 is an apocalyptic number.

999991231 is a deficient number, since it is larger than the sum of its proper divisors (1).

999991231 is an equidigital number, since it uses as much as digits as its factorization.

999991231 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 354294, while the sum is 52.

The square root of 999991231 is about 31622.6379513158. The cubic root of 999991231 is about 999.9970769915.

The spelling of 999991231 in words is "nine hundred ninety-nine million, nine hundred ninety-one thousand, two hundred thirty-one".