This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A119930 #6 Aug 24 2012 10:49:57 %S A119930 1,2,3,4,6,7,8,9,11,12,13,15,18,20,21,22,23,24,27,29,30 %N A119930 Sum of the numbers of the matrix A111490 along a boustrophedon path: a11, a11+a12, a11+a12+a21, etc. %D A119930 G. Balzarotti and P. P. Lava, Le sequenze di numeri interi, Hoepli, 2008, p. 60. %e A119930 If we rewrite the matrix putting on the top the upper left edge and then we sum the numbers following a boustrophedon path we have: %e A119930 .............1.\ %e A119930 ..........._____\ %e A119930 ........../1...1. %e A119930 ........./_________ %e A119930 .........1...2...1.\ %e A119930 ......______________\ %e A119930 ...../.1...2...1...1. %e A119930 ..../__________________ %e A119930 .....1...2...3...2...1.\ %e A119930 ..______________________\ %e A119930 ..1...2...3...1...1...1. %e A119930 then %e A119930 1, 1+1, 1+1+1, 1+1+1+1, 1+1+1+1+2, 1+1+1+1+2+1, 1+1+1+1+2+1+1, 1+1+1+1+2+1+1+1, 1+1+1+1+2+1+1+1+2, 1+1+1+1+2+1+1+1+2+1, ... %e A119930 That is 1, 2, 3, 4, 6, 7, 8, 9, 11, 12, 13, 15, 18, 20, etc. %Y A119930 Cf. A119931. %K A119930 nonn,easy %O A119930 0,2 %A A119930 _Paolo P. Lava_ and _Giorgio Balzarotti_, May 30 2006