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%I #19 Jan 28 2021 21:49:37
%S 1,4,10,28,64,140,304,640,1326,2716,5502,11052,22044,43700,86180,
%T 169184,330810,644564,1251954,2424860,4684696,9029756,17368408,
%U 33343520,63899686,122259372,233568998,445600236,849014964,1615709156,3071307852
%N Number of self-avoiding closed walks from 0 of area n in strip Z X {0,1,2}.
%D J. Labelle, Self-avoiding walks and polyominoes in strips, Bull. ICA, 23 (1998), 88-98.
%H <a href="/index/Rec#order_06">Index entries for linear recurrences with constant coefficients</a>, signature (2,1,0,-3,-2,-1).
%F G.f.: 2(1+2x^3+2x^4)/(1-x-x^2-x^3)^2-1 [Labelle]. - _Emeric Deutsch_, Apr 29 2004
%t CoefficientList[ Series[(2 + 4 x^3 + 4 x^4)/(1 - x - x^2 - x^3)^2 - 1, {x, 0, 28}], x]
%t LinearRecurrence[{2, 1, 0, -3, -2, -1}, {1, 4, 10, 28, 64, 140, 304}, 31] (* _Robert P. P. McKone_, Jan 28 2021, same method used in A038578 MMA *)
%o (PARI) Vec(2*(1+2*x^3+2*x^4)/(1-x-x^2-x^3)^2-1+ O(x^40)) \\ _Michel Marcus_, Jan 28 2021
%Y Cf. A022445, A038578.
%K nonn,walk,easy
%O 0,2
%A _N. J. A. Sloane_.
%E More terms from _Emeric Deutsch_, Apr 29 2004
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