991787949787189 has 2 divisors, whose sum is σ = 991787949787190. Its totient is φ = 991787949787188.

The previous prime is 991787949787181. The next prime is 991787949787199. The reversal of 991787949787189 is 981787949787199.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 632755561364689 + 359032388422500 = 25154633^2 + 18948150^2 .

It is an emirp because it is prime and its reverse (981787949787199) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 991787949787189 - 2³ = 991787949787181 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991787949787181) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495893974893594 + 495893974893595.

It is an arithmetic number, because the mean of its divisors is an integer number (495893974893595).

Almost surely, 2^{991787949787189} is an apocalyptic number.

It is an amenable number.

991787949787189 is a deficient number, since it is larger than the sum of its proper divisors (1).

991787949787189 is an equidigital number, since it uses as much as digits as its factorization.

991787949787189 is an evil number, because the sum of its binary digits is even.

The product of its digits is 290358577152, while the sum is 103.

The spelling of 991787949787189 in words is "nine hundred ninety-one trillion, seven hundred eighty-seven billion, nine hundred forty-nine million, seven hundred eighty-seven thousand, one hundred eighty-nine".