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 A204059 #8 Oct 13 2021 00:49:32
%S A204059 1,-1,6,-17,30,-48,170,-645,1183,-1270,5742,-22604,33462,-40868,
%T A204059 240756,-746637,1136690,-1884529,6625110,-23217030,46565244,-46627416,
%U A204059 225058682,-975425316,1356970471,-1583502622,9182205852,-26257649200,44560482150,-77433044928
%N A204059 a(n) = Pell(n) * Sum_{d|n} (-1)^(n/d) / Pell(d), where Pell(n) = A000129(n).
%F A204059 G.f.: Sum_{n>=1} x^n/(1 + A002203(n)*x^n + (-1)^n*x^(2*n)) where A002203 is the companion Pell numbers.
%F A204059 a(2*n-1) = A203797(2*n-1).
%e A204059 G.f.: A(x) = x - x^2 + 6*x^3 - 17*x^4 + 30*x^5 - 48*x^6 + 170*x^7 +...
%e A204059 where A(x) = x/(1+2*x-x^2) + x^2/(1+6*x^2+x^4) + x^3/(1+14*x^3-x^6) + x^4/(1+34*x^4+x^8) + x^5/(1+82*x^5-x^10) + x^6/(1+198*x^6+x^12) +...+ x^n/(1 + A002203(n)*x^n + (-1)^n*x^(2*n)) +...
%o A204059 (PARI) {Pell(n)=polcoeff(x/(1-2*x-x^2+x*O(x^n)),n)}
%o A204059 {a(n)=Pell(n) * sumdiv(n, d, -(-1)^(n/d)/Pell(d))}
%o A204059 (PARI) /* G.f. using companion Pell numbers: */
%o A204059 {A002203(n)=polcoeff(2*(1-x)/(1-2*x-x^2+x*O(x^n)),n)}
%o A204059 {a(n)=polcoeff(sum(m=1, n, x^m/(1 + A002203(m)*x^m + (-1)^m*x^(2*m) +x*O(x^n))), n)}
%Y A204059 Cf. A203797, A111075, A203802, A000129, A002203.
%K A204059 sign
%O A204059 1,3
%A A204059 _Paul D. Hanna_, Jan 13 2012