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 A162673 Number of different fixed (possibly) disconnected trominoes bounded (not necessarily tightly) by an n*n square 5
 0, 4, 48, 204, 580, 1320, 2604, 4648, 7704, 12060, 18040, 26004, 36348, 49504, 65940, 86160, 110704, 140148, 175104, 216220, 264180, 319704, 383548, 456504, 539400, 633100, 738504, 856548, 988204, 1134480, 1296420, 1475104, 1671648, 1887204 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Fixed quasi-trominoes. LINKS Table of n, a(n) for n=1..34. Index entries for linear recurrences with constant coefficients, signature (5,-10,10,-5,1). FORMULA a(n)=n*(n-1)*(3*n^2-3*n-2)/2. G.f.: 4*x^2*(1+7*x+x^2)/(1-x)^5. [Colin Barker, Apr 25 2012] EXAMPLE a(2)=4: the four rotations of the (connected) L tromino MATHEMATICA LinearRecurrence[{5, -10, 10, -5, 1}, {0, 4, 48, 204, 580}, 40] (* Harvey P. Dale, Aug 09 2017 *) CROSSREFS Cf. A162674, A162676, A162677, A094170 (free quasi-trominoes). Sequence in context: A366492 A275033 A192418 * A002287 A273335 A275138 Adjacent sequences: A162670 A162671 A162672 * A162674 A162675 A162676 KEYWORD nonn,easy AUTHOR David Bevan, Jul 27 2009 STATUS approved

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Last modified April 19 21:09 EDT 2024. Contains 371798 sequences. (Running on oeis4.)