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 A138268 #13 Aug 31 2025 18:40:43
%S A138268 1,4,-17,17,72,-305,305,1292,-5473,5473,23184,-98209,98209,416020,
%T A138268 -1762289,1762289,7465176,-31622993,31622993,133957148,-567451585,
%U A138268 567451585,2403763488,-10182505537,10182505537,43133785636,-182717648081,182717648081,774004377960
%N A138268 Negative of the Hankel transform of C(n) - C(n+2), where C = A000108.
%C A138268 -a(n) is the Hankel transform of C(n)-C(n+2).
%H A138268 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (-3,-8,-3,-1).
%F A138268 G.f.: (1+7*x+3*x^2+x^3)/(1+3*x+8*x^2+3*x^3+x^4).
%F A138268 a(n) = (Fibonacci(3*floor((2*n+5)/3))/Fibonacci(3))*(4*sin(2*Pi*n/3+Pi/6)/3+1/3).
%F A138268 a(0)=1, a(1)=4, a(2)=-17, a(3)=17, a(n) = -3*a(n-1)-8*a(n-2)-3*a(n-3)-a(n-4). - _Harvey P. Dale_, May 26 2011
%t A138268 LinearRecurrence[{-3,-8,-3,-1},{1,4,-17,17},41] (* or *) CoefficientList[ Series[(1+7x+3x^2+x^3)/(1+3x+8x^2+3x^3+x^4),{x,0,40}],x] (* _Harvey P. Dale_, May 26 2011 *)
%Y A138268 Cf. A000045, A000108, A001076.
%K A138268 easy,sign,changed
%O A138268 0,2
%A A138268 _Paul Barry_, Mar 10 2008
%E A138268 More terms from _Jason Yuen_, Aug 31 2025