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 A177991 #18 Jun 02 2025 02:56:38 %S A177991 1,1,1,1,1,1,1,2,1,1,1,2,1,1,1,1,3,1,2,1,1,1,3,1,2,1,1,1,1,4,1,3,1,2, %T A177991 1,1,1,4,1,3,1,2,1,1,1,1,5,1,4,1,3,1,2,1,1,1,5,1,4,1,3,1,2,1,1,1 %N A177991 Triangle read by rows, A070909 * A177990. %C A177991 Row sums = A117142: (1, 2, 3, 5, 6, 9,...) %H A177991 Peter Bala, <a href="/A177994/a177994.pdf">Matrices with repeated columns - the generalised Appell groups</a> %F A177991 As infinite lower triangular matrices, A070909 * A177990 %e A177991 First few rows of the triangle = %e A177991 1; %e A177991 1, 1; %e A177991 1, 1, 1; %e A177991 1, 2, 1, 1; %e A177991 1, 2, 1, 1, 1; %e A177991 1, 3, 1, 2, 1, 1; %e A177991 1, 3, 1, 2, 1, 1, 1; %e A177991 1, 4, 1, 3, 1, 2, 1, 1; %e A177991 1, 4, 1, 3, 1, 2, 1, 1, 1; %e A177991 1, 5, 1, 4, 1, 3, 1, 2, 1, 1; %e A177991 1, 5, 1, 4, 1, 3, 1, 2, 1, 1, 1; %e A177991 1, 6, 1, 5, 1, 4, 1, 3, 1, 2, 1, 1; %e A177991 1, 6, 1, 5, 1, 4, 1, 3, 1, 2, 1, 1, 1; %e A177991 1, 7, 1, 6, 1, 5, 1, 4, 1, 3, 1, 2, 1, 1; %e A177991 1, 7, 1, 6, 1, 5, 1, 4, 1, 3, 1, 2, 1, 1, 1; %e A177991 ... %Y A177991 A177994 = A177990 * A070909. %Y A177991 Cf. A117142. %K A177991 nonn,tabl %O A177991 0,8 %A A177991 _Gary W. Adamson_, May 16 2010 %E A177991 a(28)=1 inserted before the first "4" by _Georg Fischer_, Dec 28 2021