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 A122439 #11 Jul 30 2024 17:45:30
%S A122439 1,2,5,12,25,54,113,232,477,970,1965,3972,8001,16094,32329,64864,
%T A122439 130053,260594,521925,1044988,2091689,4185990,8375969,16757976,
%U A122439 33525165,67064346,134149981,268332404,536714129,1073503278,2147120761
%N A122439 Expansion of 1/(1-2x-x^2+4x^4).
%C A122439 Diagonal sums of number triangle A122438. Convolution of A052947 and 2^n.
%H A122439 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (2,1,0,-4).
%t A122439 CoefficientList[Series[1/(1 - 2x - x^2 + 4x^4), {x, 0, 31}], x] (* _Robert G. Wilson v_, Sep 14 2006 *)
%t A122439 LinearRecurrence[{2,1,0,-4},{1,2,5,12},40] (* _Harvey P. Dale_, Jul 30 2024 *)
%K A122439 easy,nonn
%O A122439 0,2
%A A122439 _Paul Barry_, Sep 05 2006
%E A122439 More terms from _Robert G. Wilson v_, Sep 14 2006