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 A130626 #18 Aug 05 2024 12:15:36
%S A130626 3,3,4,9,21,44,87,171,340,681,1365,2732,5463,10923,21844,43689,87381,
%T A130626 174764,349527,699051,1398100,2796201,5592405,11184812,22369623,
%U A130626 44739243,89478484,178956969,357913941,715827884,1431655767,2863311531
%N A130626 Second differences of A130624.
%C A130626 First differences of A130625: a(n) = A130625(n+1) - A130625(n).
%H A130626 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (3, -3, 2).
%F A130626 G.f.: (3-6*x+4*x^2)/((1-2*x)*(1-x+x^2)).
%F A130626 a(n) = 3a(n-1) - 3a(n-2) + 2a(n-3). - _Paul Curtz_, Apr 24 2008
%t A130626 Differences[LinearRecurrence[{3,-3,2},{0,1,5},40],2] (* or *) LinearRecurrence[{3,-3,2},{3,3,4},40] (* _Harvey P. Dale_, Aug 05 2024 *)
%o A130626 (Magma) m:=34; S:=[ [0, 1, 3][ (n-1) mod 3 +1 ]: n in [1..m] ]; T:=[ &+[ Binomial(i-1, k-1)*S[k]: k in [1..i] ]: i in [1..m] ]; U:=[ T[n+1]-T[n]: n in[1..m-1] ]; [ U[n+1]-U[n]: n in[1..m-2] ]; /* _Klaus Brockhaus_, Jun 21 2007 */
%Y A130626 Cf. A130624, A130625.
%K A130626 nonn
%O A130626 0,1
%A A130626 _Paul Curtz_, Jun 18 2007
%E A130626 Edited and extended by _Klaus Brockhaus_, Jun 21 2007