One way of "doing it in R" is to use the 'bc' command that is on most

UNIX/LINUX systems and is also on cygwin for Windows. Here are

decimal digits for 2^1000

/cygdrive/c/jph/consulting/2008-03-30: bc

bc 1.06

Copyright 1991-1994, 1997, 1998, 2000 Free Software Foundation, Inc.

This is free software with ABSOLUTELY NO WARRANTY.

For details type `warranty'.

2^1000

10715086071862673209484250490600018105614048117055336074437503883703\

51051124936122493198378815695858127594672917553146825187145285692314\

04359845775746985748039345677748242309854210746050623711418779541821\

53046474983581941267398767559165543946077062914571196477686542167660\

429831652624386837205668069376

So you can 'shell' the command from R, collect the digits and then sum them.

On Fri, Apr 4, 2008 at 10:43 AM, Rory Winston <

[hidden email]> 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,"")[[1]]))

> }

>

> This also doesnt seem to work. Is there another way I can do this in R?

> Cheers

> Rory

> --

> View this message in context:

http://www.nabble.com/Arbitrary-Precision-Numbers-tp16492549p16492549.html> Sent from the R help mailing list archive at Nabble.com.

>

> ______________________________________________

>

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>

https://stat.ethz.ch/mailman/listinfo/r-help> PLEASE do read the posting guide

http://www.R-project.org/posting-guide.html> and provide commented, minimal, self-contained, reproducible code.

>

--

Jim Holtman

Cincinnati, OH

+1 513 646 9390

What is the problem you are trying to solve?

______________________________________________

[hidden email] mailing list

https://stat.ethz.ch/mailman/listinfo/r-helpPLEASE do read the posting guide

http://www.R-project.org/posting-guide.htmland provide commented, minimal, self-contained, reproducible code.