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 A076684 #10 Apr 19 2023 00:29:14 %S A076684 1,33,609,10945,196417,3524577,63245985,1134903169,20365011073, %T A076684 365435296161,6557470319841,117669030460993,2111485077978049, %U A076684 37889062373143905,679891637638612257,12200160415121876737 %N A076684 Odd terms in A027941. %H A076684 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (19,-19,1). %F A076684 a(n) = F(6n+3) - 1 where F(k) denotes the k-th Fibonacci number. %F A076684 G.f.: (1+14x+x^2)/((1-x)(1-18x+x^2)). %t A076684 a[n_] := Fibonacci[6n+3]-1 %o A076684 (PARI) a(n)=fibonacci(6*n+3)-1 %o A076684 (PARI) a(n)=if(n<0,0,subst(poltchebi(n)+poltchebi(n+1),x,9)/5-1) %Y A076684 Cf. A027941, A000045. %K A076684 nonn,easy %O A076684 0,2 %A A076684 _Benoit Cloitre_, Oct 25 2002