1991807556 has 12 divisors (see below), whose sum is σ = 4647550992. Its totient is φ = 663935848.

The previous prime is 1991807513. The next prime is 1991807579. The reversal of 1991807556 is 6557081991.

It is a tau number, because it is divible by the number of its divisors (12).

It is a junction number, because it is equal to n+sod(n) for n = 1991807499 and 1991807508.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 82991970 + ... + 82991993.

It is an arithmetic number, because the mean of its divisors is an integer number (387295916).

Almost surely, 2^1991807556 is an apocalyptic number.

It is an amenable number.

1991807556 is an abundant number, since it is smaller than the sum of its proper divisors (2655743436).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

1991807556 is a wasteful number, since it uses less digits than its factorization.

1991807556 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 165983970 (or 165983968 counting only the distinct ones).

The product of its (nonzero) digits is 680400, while the sum is 51.

The square root of 1991807556 is about 44629.6712513099. The cubic root of 1991807556 is about 1258.1983901762.

The spelling of 1991807556 in words is "one billion, nine hundred ninety-one million, eight hundred seven thousand, five hundred fifty-six".