19999891 has 2 divisors, whose sum is σ = 19999892. Its totient is φ = 19999890.

The previous prime is 19999873. The next prime is 19999897. The reversal of 19999891 is 19899991.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 19999891 - 2⁹ = 19999379 is a prime.

It is not a weakly prime, because it can be changed into another prime (19999897) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9999945 + 9999946.

It is an arithmetic number, because the mean of its divisors is an integer number (9999946).

Almost surely, 2^19999891 is an apocalyptic number.

19999891 is a deficient number, since it is larger than the sum of its proper divisors (1).

19999891 is an equidigital number, since it uses as much as digits as its factorization.

19999891 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 472392, while the sum is 55.

The square root of 19999891 is about 4472.1237684125. The cubic root of 19999891 is about 271.4412685394.

The spelling of 19999891 in words is "nineteen million, nine hundred ninety-nine thousand, eight hundred ninety-one".