199981891 has 2 divisors, whose sum is σ = 199981892. Its totient is φ = 199981890.

The previous prime is 199981889. The next prime is 199981907. The reversal of 199981891 is 198189991.

It is a weak prime.

It is an emirp because it is prime and its reverse (198189991) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 199981891 - 2¹ = 199981889 is a prime.

Together with 199981889, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (199981811) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 99990945 + 99990946.

It is an arithmetic number, because the mean of its divisors is an integer number (99990946).

Almost surely, 2^199981891 is an apocalyptic number.

199981891 is a deficient number, since it is larger than the sum of its proper divisors (1).

199981891 is an equidigital number, since it uses as much as digits as its factorization.

199981891 is an evil number, because the sum of its binary digits is even.

The product of its digits is 419904, while the sum is 55.

The square root of 199981891 is about 14141.4953594024. The cubic root of 199981891 is about 584.7858967641.

The spelling of 199981891 in words is "one hundred ninety-nine million, nine hundred eighty-one thousand, eight hundred ninety-one".