199990991 has 2 divisors, whose sum is σ = 199990992. Its totient is φ = 199990990.

The previous prime is 199990981. The next prime is 199990993. The reversal of 199990991 is 199099991.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 199990991 - 2¹⁸ = 199728847 is a prime.

Together with 199990993, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (199990993) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 99995495 + 99995496.

It is an arithmetic number, because the mean of its divisors is an integer number (99995496).

Almost surely, 2^199990991 is an apocalyptic number.

199990991 is a deficient number, since it is larger than the sum of its proper divisors (1).

199990991 is an equidigital number, since it uses as much as digits as its factorization.

199990991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 531441, while the sum is 56.

The square root of 199990991 is about 14141.8171038944. The cubic root of 199990991 is about 584.7947666855.

The spelling of 199990991 in words is "one hundred ninety-nine million, nine hundred ninety thousand, nine hundred ninety-one".