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 A234349 #20 Jul 27 2015 13:27:24 %S A234349 1,3,4,6,7,8,10,11,12,13,15,16,17,19,20,22,23,24,25,27,28 %N A234349 Maximal number of points that can be placed on a triangular grid of side n so that no three points are collinear. %C A234349 Length of the n-th row in triangle A194136 and triangle A234350. %C A234349 Differs from A007401 first at n=14. %e A234349 In a triangular grid of side 5 at most 7 points (x) can be placed so that no three of them are on a straight line. (There are exactly 2 ways to do it, rotations and reflections ignored.) %e A234349 . x %e A234349 . x . . %e A234349 x . x x . x %e A234349 x . x . . x x . %e A234349 . x . x . . x . x . %Y A234349 Cf. A194136, A234350. %K A234349 nonn,hard,more %O A234349 1,2 %A A234349 _Heinrich Ludwig_, Dec 24 2013 %E A234349 a(13)-a(14) from _Heinrich Ludwig_, Jan 10 2014 %E A234349 a(15)-a(16) from _Heinrich Ludwig_, Jan 28 2014 %E A234349 a(17)-a(21) from _Rob Pratt_, Jul 27 2015