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 A129684 #7 Jul 19 2019 14:26:39 %S A129684 1,0,1,1,0,1,0,3,0,1,6,0,6,0,1,0,30,0,10,0,1,90,0,90,0,15,0,1,0,630,0, %T A129684 210,0,21,0,1,2520,0,2520,0,420,0,28,0,1,0,22680,0,7560,0,756,0,36,0, %U A129684 1,113400,0,113400,0,18900,0,1260,0,45,0,1 %N A129684 Exponential Riordan array [1/(1-x^2/2), x]. %C A129684 Row sums are A087214. Inverse is A129685. %F A129684 Number triangle T(n,k) = [k<=n](n!/k!)*(1/2^((n-k)/2))*(1+(-1)^(n-k))/2. %e A129684 Triangle begins %e A129684 1, %e A129684 0, 1, %e A129684 1, 0, 1, %e A129684 0, 3, 0, 1, %e A129684 6, 0, 6, 0, 1, %e A129684 0, 30, 0, 10, 0, 1, %e A129684 90, 0, 90, 0, 15, 0, 1, %e A129684 0, 630, 0, 210, 0, 21, 0, 1 %t A129684 (* The function RiordanArray is defined in A256893. *) %t A129684 RiordanArray[1/(1 - #^2/2)&, #&, 11, True] // Flatten (* _Jean-François Alcover_, Jul 19 2019 *) %Y A129684 Cf. A087214, A129685. %K A129684 easy,nonn,tabl %O A129684 0,8 %A A129684 _Paul Barry_, Apr 28 2007