[Jprogramming] Another Quora Problem

[Murray Eisenberg]

The sum in question is twice the sum of the integers from 1 to 21. By the well-known formula (sometimes attributed to Gauss), the latter sum is half the product of 21 and 21 + 1, so the sum in question is 

    */21+i. 2
462


> On28 Aug 2017 12:02:57 -0500,S kip Cave <skip at caveconsulting.com <mailto:skip at caveconsulting.com>> wrote:
> 
> A simple problem posted on Quora:
> 
> What is the sum of all the even numbers from 2 to 42?
> 
> My J solution:
>   a=:>:i.42
>  +/(-.2|a)#a
> 462
> 
> I'm sure this can be done in a single line using a hook or fork.
> but I'm not clear enough with the train rules to put this all together
> on a single line.
> Any suggestions?

——
Murray Eisenberg                                murray at math.umass.edu
Mathematics & Statistics Dept.       
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