181663991 has 2 divisors, whose sum is σ = 181663992. Its totient is φ = 181663990.

The previous prime is 181663981. The next prime is 181664017. The reversal of 181663991 is 199366181.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 181663991 - 2¹⁰ = 181662967 is a prime.

It is a Sophie Germain prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (181663961) 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, 90831995 + 90831996.

It is an arithmetic number, because the mean of its divisors is an integer number (90831996).

Almost surely, 2^181663991 is an apocalyptic number.

181663991 is a deficient number, since it is larger than the sum of its proper divisors (1).

181663991 is an equidigital number, since it uses as much as digits as its factorization.

181663991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 69984, while the sum is 44.

The square root of 181663991 is about 13478.2784879969. The cubic root of 181663991 is about 566.3561450196.

The spelling of 181663991 in words is "one hundred eighty-one million, six hundred sixty-three thousand, nine hundred ninety-one".