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 A038249 #11 Jun 13 2015 00:49:19 %S A038249 1,2,9,19,75,160,622,1329,5157,11021,42756,91376,354484,757588, %T A038249 2938977,6281058,24366645,52075371,202020427,431749580,1674922950, %U A038249 3579575053,13886550633,29677753369,115131438424,246054079584,954538564968 %N A038249 Third line of 4-wave sequence A038197. %H A038249 F. v. Lamoen, <a href="http://home.wxs.nl/~lamoen/wiskunde/wave.htm">Wave sequences</a> %H A038249 <a href="/index/Rec#order_08">Index entries for linear recurrences with constant coefficients</a>, signature (0,10,0,-15,0,7,0,-1). %F A038249 G.f.: (-x^3-x^2+2*x+1) / (x^8-7*x^6+15*x^4-10*x^2+1). - _Alois P. Heinz_, Jul 16 2009 %p A038249 a:= n-> (Matrix([[ `if`(irem(n,2)=0, 1, 2), 0, 0, 1]]). Matrix(4, (i,j)-> if i=j-1 then 1 elif j=1 then [10, -15, 7, -1][i] else 0 fi)^iquo(n, 2))[1,1]: seq(a(n), n=0..30); # _Alois P. Heinz_, Jul 16 2009 %K A038249 nonn,easy %O A038249 0,2 %A A038249 _Floor van Lamoen_