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 A380617 #4 Jan 28 2025 20:51:14 %S A380617 1,1,1,2,2,1,5,8,5,2,16,28,26,12,3,53,121,128,82,28,6,206,528,686,505, %T A380617 239,68,10,817,2516,3638,3192,1802,686,157,20,3620,12302,20250,19976, %U A380617 13268,6078,1876,372,35,16361,63643,114669,126876,95422,50954,19346,5100,845,70 %N A380617 Triangle read by rows: T(n,k) is the number of achiral combinatorial maps with n edges and k vertices, 1 <= k <= n + 1. %C A380617 By duality, also the number of achiral combinatorial maps with n edges and k faces. %e A380617 Triangle begins: %e A380617 n\k | 1 2 3 4 5 6 7 8 9 %e A380617 ----+------------------------------------------------------- %e A380617 0 | 1; %e A380617 1 | 1, 1; %e A380617 2 | 2, 2, 1; %e A380617 3 | 5, 8, 5, 2; %e A380617 4 | 16, 28, 26, 12, 3; %e A380617 5 | 53, 121, 128, 82, 28, 6; %e A380617 6 | 206, 528, 686, 505, 239, 68, 10; %e A380617 7 | 817, 2516, 3638, 3192, 1802, 686, 157, 20; %e A380617 8 | 3620, 12302, 20250, 19976, 13268, 6078, 1876, 372, 35; %e A380617 ... %Y A380617 Row sums are A170947. %Y A380617 Main diagonal is A001405(n-1). %Y A380617 Column 1 is A018191. %Y A380617 Cf. A379431 (planar), A380615 (sensed), A380616 (unsensed). %K A380617 nonn,tabl %O A380617 0,4 %A A380617 _Andrew Howroyd_, Jan 28 2025