6391991817 has 6 divisors (see below), whose sum is σ = 9232877082. Its totient is φ = 4261327872.

The previous prime is 6391991797. The next prime is 6391991849. The reversal of 6391991817 is 7181991936.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 6269314041 + 122677776 = 79179^2 + 11076^2 .

It is not a de Polignac number, because 6391991817 - 2¹⁹ = 6391467529 is a prime.

It is a super-2 number, since 2×6391991817² = 81715118777189922978, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (6391996817) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 355110648 + ... + 355110665.

It is an arithmetic number, because the mean of its divisors is an integer number (1538812847).

Almost surely, 2^6391991817 is an apocalyptic number.

It is an amenable number.

6391991817 is a deficient number, since it is larger than the sum of its proper divisors (2840885265).

6391991817 is a wasteful number, since it uses less digits than its factorization.

6391991817 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 710221319 (or 710221316 counting only the distinct ones).

The product of its digits is 734832, while the sum is 54.

The square root of 6391991817 is about 79949.9331894655. The cubic root of 6391991817 is about 1855.8608207950.

The spelling of 6391991817 in words is "six billion, three hundred ninety-one million, nine hundred ninety-one thousand, eight hundred seventeen".