1991518775 has 12 divisors (see below), whose sum is σ = 2492565912. Its totient is φ = 1578323040.

The previous prime is 1991518759. The next prime is 1991518783. The reversal of 1991518775 is 5778151991.

It is not a de Polignac number, because 1991518775 - 2⁴ = 1991518759 is a prime.

It is a super-6 number, since 6×1991518775⁶ (a number of 57 digits) contains 666666 as substring. Note that it is a super-d number also for d = 2.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

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 in 11 ways as a sum of consecutive naturals, for example, 369572 + ... + 374921.

It is an arithmetic number, because the mean of its divisors is an integer number (207713826).

Almost surely, 2^1991518775 is an apocalyptic number.

1991518775 is a deficient number, since it is larger than the sum of its proper divisors (501047137).

1991518775 is a wasteful number, since it uses less digits than its factorization.

1991518775 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 744610 (or 744605 counting only the distinct ones).

The product of its digits is 793800, while the sum is 53.

The square root of 1991518775 is about 44626.4358312424. The cubic root of 1991518775 is about 1258.1375808627.

The spelling of 1991518775 in words is "one billion, nine hundred ninety-one million, five hundred eighteen thousand, seven hundred seventy-five".