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 <[email protected]
> <mailto:[email protected]>> 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 [email protected]
Mathematics & Statistics Dept.
Lederle Graduate Research Tower phone 240 246-7240 (H)
University of Massachusetts
710 North Pleasant Street
Amherst, MA 01003-9305
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