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 A171556 #10 May 26 2025 23:51:07 %S A171556 1,1,4,13,40,124,394,1285,4288,14584,50386,176356,624034,2228698, %T A171556 8023318,29084533,106073008,388934368,1432916098,5301789568, %U A171556 19692361258,73398801058,274447690918,1029178840948,3869712441970,14585839204354 %N A171556 a(n) = 3*C(n)-2, where C(n) = A000108(n). %C A171556 Hankel transform is A171557. %F A171556 G.f.: 3*(1-sqrt(1-4*x))/(2*x)-2/(1-x). %F A171556 Starting with offset 1 = Narayana transform (A001263) of [1,3,3,3,...]. - _Gary W. Adamson_, Jul 29 2011 %F A171556 Conjecture: (n+1)*(n-2)*a(n) +(-5*n^2+11*n-4)*a(n-1) +2*(n-1)*(2*n-3)*a(n-2)=0. - _R. J. Mathar_, Sep 30 2012 %K A171556 easy,nonn %O A171556 0,3 %A A171556 _Paul Barry_, Dec 11 2009