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 A171999 #5 Mar 22 2013 14:58:34 %S A171999 1,1,2,1,3,6,1,4,6,12,1,5,10,20,30,1,6,15,20,30,60,90,1,7,21,35,42, %T A171999 105,140,210,1,8,28,56,70,168,280,420,560,1,9,36,72,84,126,252,504, %U A171999 630,756,1260,1680,1,10,45,90,120,210,252,360,840,1260,2520,3150,4200,1,11,55 %N A171999 Triangle of trinomial coefficients. %C A171999 Number of numbers in row n is given by A086753. %C A171999 Row sums: A092255. %C A171999 See A046816, Pascal's pyramid of trinomial coefficients. %e A171999 First six rows: %e A171999 1 %e A171999 1...2 %e A171999 1...3...6 %e A171999 1...4...6....12 %e A171999 1...5...10...20...30 %e A171999 1...6...15...20...30...60...90 %Y A171999 Cf. A036038, A046816, A092255. %K A171999 nonn,tabf %O A171999 1,3 %A A171999 _Clark Kimberling_, Jan 21 2010