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 A119931 #7 Aug 24 2012 10:49:57 %S A119931 1,2,3,4,6,7,8,10,11,12,13,15,18,20,21,22,24,27,28,29,30 %N A119931 Sum of the numbers of the matrix A111490 along a boustrophedon path: a11, a11+a21, a11+a21+a21, etc. %D A119931 G. Balzarotti and P. P. Lava, Le sequenze di numeri interi, Hoepli, 2008, p. 60. %e A119931 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 A119931 .........../.1. %e A119931 ........../_____ %e A119931 ...........1...1.\ %e A119931 ........._________\ %e A119931 ......./.1...2...1. %e A119931 ....../______________ %e A119931 .......1...2...1...1.\ %e A119931 ....._________________\ %e A119931 .../.1...2...3...2...1. %e A119931 ../_____________________ %e A119931 ...1...2...3...1...1...1. %e A119931 then %e A119931 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+2, 1+1+1+1+2+1+1+2+1, 1+1+1+1+2+1+1+2+1+1, ... %e A119931 That is 1, 2, 3, 4, 6, 7, 8, 10, 11, 12, 13, 15, 18, 20, etc. %Y A119931 Cf. A119930. %K A119931 nonn,easy %O A119931 0,2 %A A119931 _Paolo P. Lava_ and _Giorgio Balzarotti_, May 30 2006