1991943817 has 2 divisors, whose sum is σ = 1991943818. Its totient is φ = 1991943816.

The previous prime is 1991943787. The next prime is 1991943829. The reversal of 1991943817 is 7183491991.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1129699321 + 862244496 = 33611^2 + 29364^2 .

It is a cyclic number.

It is not a de Polignac number, because 1991943817 - 2⁷ = 1991943689 is a prime.

It is not a weakly prime, because it can be changed into another prime (1991943847) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 995971908 + 995971909.

It is an arithmetic number, because the mean of its divisors is an integer number (995971909).

Almost surely, 2^1991943817 is an apocalyptic number.

It is an amenable number.

1991943817 is a deficient number, since it is larger than the sum of its proper divisors (1).

1991943817 is an equidigital number, since it uses as much as digits as its factorization.

1991943817 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 489888, while the sum is 52.

The square root of 1991943817 is about 44631.1977992973. The cubic root of 1991943817 is about 1258.2270809436.

It can be divided in two parts, 19919 and 43817, that added together give a palindrome (63736).

The spelling of 1991943817 in words is "one billion, nine hundred ninety-one million, nine hundred forty-three thousand, eight hundred seventeen".