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 A238828 a(0)=0; thereafter a(n) = A238824(n-1)+A238825(n). 7

%I

%S 0,0,1,2,5,12,28,70,169,420,1030,2546,6266,15452,38056,93774,230993,

%T 569084,1401913,3453690,8508214,20960336,51636447,127208350,313382262,

%U 772028708,1901920456,4685449914,11542774524,28436041324,70053211913,172578611878

%N a(0)=0; thereafter a(n) = A238824(n-1)+A238825(n).

%H Vincenzo Librandi, <a href="/A238828/b238828.txt">Table of n, a(n) for n = 1..1000</a>

%H V. M. Zhuravlev, <a href="http://www.mccme.ru/free-books/matpros/mph.pdf">Horizontally-convex polyiamonds and their generating functions</a>, Mat. Pros. 17 (2013), 107-129 (in Russian). See the sequence b(n).

%H <a href="/index/Rec#order_08">Index entries for linear recurrences with constant coefficients</a>, signature (2,3,-4,-3,2,4,2,-1).

%F G.f.: x^3*(1-2*x^2+2*x^5) / ( (1+x)*(x^7-3*x^6-x^5-x^4+4*x^3-3*x+1) ). - _R. J. Mathar_, Mar 20 2014

%p g:=proc(n) option remember; local t1;

%p t1:=[2,3,6,14,34,84,208,515];

%p if n <= 7 then t1[n] else

%p 3*g(n-1)-4*g(n-3)+g(n-4)+g(n-5)+3*g(n-6)-g(n-7); fi; end proc;

%p [seq(g(n),n=1..32)]; # A238823

%p d:=proc(n) option remember; global g; local t1;

%p t1:=[0,1];

%p if n <= 2 then t1[n] else

%p g(n-1)-2*d(n-1)-d(n-2); fi; end proc;

%p [seq(d(n),n=1..32)]; # A238824

%p p:=proc(n) option remember; global d; local t1;

%p t1:=[0,0,0,1];

%p if n <= 4 then t1[n] else

%p p(n-2)+p(n-3)+2*(d(n-3)+d(n-4)); fi; end proc;

%p [seq(p(n),n=1..32)]; # A238825

%p [seq(p(n+3)-p(n+1),n=1..32)]; #A238826

%p r:=proc(n) option remember; global p; local t1;

%p t1:=[0,0,0,0];

%p if n <= 4 then t1[n] else

%p r(n-2)+p(n-3); fi; end proc;

%p [seq(r(n),n=1..32)]; # A238827

%p [0,seq(d(n-1)+p(n),n=2..32)]; #A238828

%t CoefficientList[Series[x^2 (1 - 2 x^2 + 2 x^5)/((1 + x) (x^7 - 3 x^6 - x^5 - x^4 + 4 x^3 - 3 x + 1)), {x, 0, 40}], x] (* _Vincenzo Librandi_, Mar 21 2014 *)

%o (MAGMA) m:=40; R<x>:=LaurentSeriesRing(RationalField(), m); [0,0] cat Coefficients(R! x^3*(1-2*x^2+2*x^5) / ( (1+x)*(x^7-3*x^6-x^5-x^4+4*x^3-3*x+1))); // _Vincenzo Librandi_, Mar 21 2014

%Y Cf. A238823-A238827.

%K nonn,easy

%O 1,4

%A _N. J. A. Sloane_, Mar 08 2014

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Last modified August 25 03:10 EDT 2019. Contains 326318 sequences. (Running on oeis4.)