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 A103644 #29 Mar 07 2024 14:13:43
%S A103644 1,1,4,25,1,256,169,1225,5476,961,64009,25600,358801,1164241,515524,
%T A103644 15642025,3243601,101284096,239228089,216825625,3736387876,287336401,
%U A103644 27697946329,47210598400
%N A103644 Expansion of g.f. (3x+1)/((1-3*x)*(1+5*x+9*x^2)).
%C A103644 A floretion-generated sequence of squares.
%C A103644 This sequence is also related to several other sequences of squares.
%H A103644 Harvey P. Dale, <a href="/A103644/b103644.txt">Table of n, a(n) for n = 0..1000</a>
%H A103644 Creighton Dement, <a href="http://fumba.eu/sitelayout/Floretion.php">Online Floretion Multiplier</a>. [broken link]
%H A103644 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (-2,6,27).
%F A103644 a(n+3) = -2a(n+2) + 6a(n+1) + 27a(n), a(0) = 1, a(1) = 1, a(2) = 4.
%F A103644 a(n) = (1/11)*(2*3^n-(-5/2-(I*sqrt(11))/2)^n-(-5/2+(I*sqrt(11))/2)^n). [_Creighton Dement_, May 24 2009]
%F A103644 11*a(n) = 6*3^n + 5*b(n) + 18*b(n-1) where b(n) = (-1)^n*A190970(n+1). - _R. J. Mathar_, Mar 23 2023
%p A103644 A103644 := proc(n)
%p A103644 6*3^n+5*(-1)^n*A190970(n+1)+18*(-1)^(n+1)*A190970(n) ;
%p A103644 %/11 ;
%p A103644 end proc:
%p A103644 seq(A103644(n),n=0..20) ; # _R. J. Mathar_, Mar 23 2023
%t A103644 CoefficientList[Series[(3x+1)/(1+2x-6x^2-27x^3),{x,0,30}],x] (* or *) LinearRecurrence[{-2,6,27},{1,1,4},30] (* _Harvey P. Dale_, Dec 13 2017 *)
%Y A103644 Cf. A103645.
%K A103644 nonn,easy
%O A103644 0,3
%A A103644 _Creighton Dement_, Feb 11 2005
%E A103644 Corrected by _T. D. Noe_, Nov 07 2006