199999991 has 2 divisors, whose sum is σ = 199999992. Its totient is φ = 199999990.

The previous prime is 199999963. The next prime is 200000033.

199999991 is nontrivially palindromic in base 10.

It is a weak prime.

It is a palprime.

It is a cyclic number.

It is not a de Polignac number, because 199999991 - 2¹⁸ = 199737847 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (199999901) 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, 99999995 + 99999996.

It is an arithmetic number, because the mean of its divisors is an integer number (99999996).

Almost surely, 2^199999991 is an apocalyptic number.

199999991 is a deficient number, since it is larger than the sum of its proper divisors (1).

199999991 is an equidigital number, since it uses as much as digits as its factorization.

199999991 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 4782969, while the sum is 65.

The square root of 199999991 is about 14142.1353055329. The cubic root of 199999991 is about 584.8035388705.

The spelling of 199999991 in words is "one hundred ninety-nine million, nine hundred ninety-nine thousand, nine hundred ninety-one".