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 A144021 #7 Dec 29 2023 10:22:29 %S A144021 1,2,1,1,2,3,2,1,6,6,1,2,3,12,15,2,1,6,6,30,33,1,2,3,12,15,66,78,2,1, %T A144021 6,6,30,33,156,177,1,2,3,12,15,66,78,354,411,2,1,6,6,30,33,156,177, %U A144021 822,942 %N A144021 Eigentriangle by rows, T(n,k) = A000034(n-k+1)*A105476(k-1). %C A144021 Row sums = A105476: (1, 3, 6, 15, 33, 78,...). %C A144021 Left column = A000034: (1, 2, 1, 2, 1, 2,...). %C A144021 Right border = A105476 shifted: (1, 1, 3, 6, 15, 33, 78,...). %F A144021 Eigentriangle by rows, A000034(n-k+1)*A105476(k-1); where A105476(k-1) = A105476 shifted = (1, 1, 3, 6, 15, 33, 78, 177,...). %e A144021 First few rows of the triangle = %e A144021 1; %e A144021 2, 1; %e A144021 1, 2, 3 %e A144021 2, 1, 6, 6 %e A144021 1, 2, 3, 12, 15 %e A144021 2, 1, 6, 6, 30, 33; %e A144021 1, 2, 3, 12, 15, 66, 78 %e A144021 2, 1, 6, 6, 30, 33, 156, 177; %e A144021 1, 2, 3, 12, 15, 66, 78, 354, 411; %e A144021 ... %e A144021 Row 4 = (2, 1, 6, 6) = termwise product of (2, 1, 2, 1) and (1, 1, 3, 6) = (2*1, 1*1, 2*3, 1*6). %Y A144021 Cf. A000034, A105476. %K A144021 nonn %O A144021 1,2 %A A144021 _Gary W. Adamson_, Sep 07 2008