1991863 has 2 divisors, whose sum is σ = 1991864. Its totient is φ = 1991862.

The previous prime is 1991861. The next prime is 1991879. The reversal of 1991863 is 3681991.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 1991863 - 2¹ = 1991861 is a prime.

Together with 1991861, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1991861) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 995931 + 995932.

It is an arithmetic number, because the mean of its divisors is an integer number (995932).

2^1991863 is an apocalyptic number.

1991863 is a deficient number, since it is larger than the sum of its proper divisors (1).

1991863 is an equidigital number, since it uses as much as digits as its factorization.

1991863 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 11664, while the sum is 37.

The square root of 1991863 is about 1411.3337663359. Note that the first 3 decimals coincide. The cubic root of 1991863 is about 125.8210064481.

The spelling of 1991863 in words is "one million, nine hundred ninety-one thousand, eight hundred sixty-three".