1991137777 has 4 divisors (see below), whose sum is σ = 1993282020. Its totient is φ = 1988993536.

The previous prime is 1991137769. The next prime is 1991137873. The reversal of 1991137777 is 7777311991.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 7777311991 = 467 ⋅16653773.

It can be written as a sum of positive squares in 2 ways, for example, as 636603361 + 1354534416 = 25231^2 + 36804^2 .

It is a cyclic number.

It is not a de Polignac number, because 1991137777 - 2³ = 1991137769 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1991137717) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1070728 + ... + 1072585.

It is an arithmetic number, because the mean of its divisors is an integer number (498320505).

Almost surely, 2^1991137777 is an apocalyptic number.

It is an amenable number.

1991137777 is a deficient number, since it is larger than the sum of its proper divisors (2144243).

1991137777 is an equidigital number, since it uses as much as digits as its factorization.

1991137777 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2144242.

The product of its digits is 583443, while the sum is 52.

The square root of 1991137777 is about 44622.1668792541. The cubic root of 1991137777 is about 1258.0573441979.

The spelling of 1991137777 in words is "one billion, nine hundred ninety-one million, one hundred thirty-seven thousand, seven hundred seventy-seven".