From: jim holtman <jholtman_at_gmail.com>

Date: Fri, 04 Apr 2008 20:26:31 -0500

Date: Fri, 04 Apr 2008 20:26:31 -0500

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 <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,"")[[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.
**>
**> ______________________________________________
**> R-help_at_r-project.org mailing list
**> 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? ______________________________________________ R-help_at_r-project.org mailing list 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.Received on Sat 05 Apr 2008 - 01:32:01 GMT

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