# [R] Arbitrary Precision Numbers

Gabor Grothendieck ggrothendieck at gmail.com
Sat Apr 5 03:55:22 CEST 2008

```Have a look at the Ryacas package which interfaces R to yacas.
yacas can do exact arithmetic.

On Fri, Apr 4, 2008 at 11:43 AM, Rory Winston <rory.winston at gmail.com> wrote:
>
> Hi
>
> (If you're wondering, this is a Project Euler question :))
>
> If I wanted to calculate the sum of the digits in the decimal representation
> of 2^1000, what would be a good way to go about that? I've tried the
> following methods:
>
> # Calculate the sum of digits in the decimal representation of 2^n
> # Only works for smaller values of n
> bsum <- function(n) {
>        s <- 0
>        e <- floor(log10(2^n))
>        for (i in seq(e,0,-1)) {
>                s <- s + (((2^n) %/% 10^i) %% 10)
>        }
>        s
> }
>
> The above doesnt work, as I am using an integer modulus which has
> insufficient precision. so I tried to coerce R to produce a full-precision
> integer and sum the digits of that:
>
> bsum2 <- function(n) {
>        s <- 0
>        strn <- formatC(2^n, format="fg")
>        sum(as.numeric(strsplit(strn,"")[]))
> }
>
> This also doesnt seem to work. Is there another way I can do this in R?
> Cheers
> Rory
> --
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