Nice Ric, Slight variation, although we are getting a bit away from the original question it is still fun to play with the patterns. sumPrimes1=: [: +/i.&.(p:inv) sumPrimes1 20 77 Cheers, bob On Apr 29, 2014, at 9:21 AM, Ric Sherlock <tikkanz at gmail.com> wrote: > sumPrimes=: +/@:p:@i.@(p:inv)