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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
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
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.)