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 A131779 #5 Sep 08 2018 16:07:28
%S A131779 1,3,1,1,3,1,3,1,5,1,1,3,5,5,1,3,1,9,5,7,1,1,3,9,9,11,7,1,3,1,13,9,21,
%T A131779 11,9,1,1,3,13,13,29,21,19,9,1,3,1,17,13,43,29,41,19,11,1,1,3,17,17,
%U A131779 55,43,69,41,29,11,1,3,1,21,17,73,55,113,69,71,29,13,1
%N A131779 Triangle read by rows: T(n,k) = 2*A065941(n-1,k-1) - (-1)^(n+k).
%H A131779 Andrew Howroyd, <a href="/A131779/b131779.txt">Table of n, a(n) for n = 1..1275</a> (first 50 rows)
%F A131779 T(n,k) = 2*binomial(n-1-floor(k/2), floor((k-1)/2)) - (-1)^(n+k). - _Andrew Howroyd_, Sep 08 2018
%e A131779 First few rows of the triangle are:
%e A131779 1;
%e A131779 3, 1;
%e A131779 1, 3, 1;
%e A131779 3, 1, 5, 1;
%e A131779 1, 3, 5, 5, 1;
%e A131779 3, 1, 9, 5, 7, 1;
%e A131779 1, 3, 9, 9, 11, 7, 1;
%e A131779 ...
%o A131779 (PARI) T(n,k) = {if(k<=n, 2*binomial(n-1-k\2, (k-1)\2) - (-1)^(n+k), 0)} \\ _Andrew Howroyd_, Sep 08 2018
%Y A131779 Row sums are A131780.
%Y A131779 Cf. A065941.
%K A131779 nonn,tabl
%O A131779 1,2
%A A131779 _Gary W. Adamson_, Jul 14 2007
%E A131779 a(28)-a(29) corrected and terms a(56) and beyond from _Andrew Howroyd_, Sep 08 2018