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Re: Summation question

  • To: mathgroup at smc.vnet.net
  • Subject: [mg85727] Re: Summation question
  • From: David Bailey <dave at Remove_Thisdbailey.co.uk>
  • Date: Wed, 20 Feb 2008 06:57:49 -0500 (EST)
  • References: <fpdu7v$qlq$1@smc.vnet.net>

Robert Pigeon wrote:
> Good day all,
> 
>             I want to make a summation like this:  Sum[f[i],{i, start,
> finish}]. What I want is that the sum be over a specific set like
> {1,3,5,7,11,13}. So the sum would be : f[1]+f[3]+f[5]+f[7]+f[11]+f[13]. The
> set I want to use is the primes. So, how do I use, if possible, Sum over a
> specific set ?
> 
>  
> 
> Thanks,
> 
>  
> 
> Robert
> 
>  
> 
> Robert Pigeon
> 
> 
Given that you have a list of positions at which you want the sum - 
{1,3,5,7,11,13}, why not use Map, and then convert the resultant list to 
a summation:

Plus @@ Map[f, {1, 3, 5, 7, 11, 13}]

BTW, isn't 2 a prime too!

David Bailey
http://www.dbaileyconsultancy.co.uk


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