18115991 has 2 divisors, whose sum is σ = 18115992. Its totient is φ = 18115990.

The previous prime is 18115969. The next prime is 18116017. The reversal of 18115991 is 19951181.

It is a weak prime.

It is an emirp because it is prime and its reverse (19951181) is a distict prime.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-18115991 is a prime.

It is a Sophie Germain prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (18115901) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9057995 + 9057996.

It is an arithmetic number, because the mean of its divisors is an integer number (9057996).

Almost surely, 2^18115991 is an apocalyptic number.

18115991 is a deficient number, since it is larger than the sum of its proper divisors (1).

18115991 is an equidigital number, since it uses as much as digits as its factorization.

18115991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3240, while the sum is 35.

The square root of 18115991 is about 4256.2884065815. The cubic root of 18115991 is about 262.6358649653.

The spelling of 18115991 in words is "eighteen million, one hundred fifteen thousand, nine hundred ninety-one".