https://oeis.org/A118141
"A parity pattern is a matrix of 0's and 1's with the property that every 0 is adjacent to an even number of 1's and every 1 is adjacent to an odd number of 1's." As a J exercise, I've defined a verb that creates a parity pattern when given its height and the first row. tripsums=: 3: +/\ (0&, @: ,&0) nextrow=: 2: | (+ tripsums) grow=: , _2&{ nextrow {: addzeros=: ,:~ ~:~ paritypattern=: ([: }. grow@:]^:(<: @: [)) addzeros 4 paritypattern 0 0 1 1 0 0 1 1 0 1 0 0 1 1 0 1 0 1 0 1 I would love to see other approaches to this problem. - Ivan ---------------------------------------------------------------------- For information about J forums see http://www.jsoftware.com/forums.htm