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 A115138 #5 Sep 05 2025 13:28:26 %S A115138 1,-1,1,15,113,783,5361,36879,255985,1794063,12689393,90505231, %T A115138 650379249,4705157135,34244198385,250572963855,1842382110705, %U A115138 13605619630095,100872203796465,750556607938575,5602962592235505,41952165966643215,314983352736153585 %N A115138 A sequence related to Catalan numbers A000108. %C A115138 See also A115150, the third diagonal of triangle A113647 (called Y(2,1)). %F A115138 (1-4*x)*(2*c(2*x)-1)/(1+x) with c(x) g.f. of A000108 (Catalan). %F A115138 a(n) = A113647(n, n-1), n>=2. %F A115138 a(n) = b(n)-4*b(n-1) with b(n) := A062992(n), n>=2; a(0)=1, a(1)=-1. %e A115138 15 = a(3) = A062992(3) - 4*A062992(2) = 67 - 4*13. %Y A115138 Cf. A000108, A062992. %Y A115138 Cf. A113647, A115150. %K A115138 sign,easy,changed %O A115138 0,4 %A A115138 _Wolfdieter Lang_, Jan 13 2006