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 A134437 Number of cells in the 2nd rows of all deco polyominoes of height n. A deco polyomino is a directed column-convex polyomino in which the height, measured along the diagonal, is attained only in the last column. 2
 0, 1, 7, 45, 312, 2400, 20520, 194040, 2016000, 22861440, 281232000, 3732220800, 53169177600, 809512704000, 13120332825600, 225573828480000, 4100866818048000, 78606921609216000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,3 COMMENTS a(n) = Sum_{k=0..n-1} k*A134436(n,k). REFERENCES E. Barcucci, A. del Lungo and R. Pinzani, "Deco" polyominoes, permutations and random generation, Theoretical Computer Science, 159, 1996, 29-42. LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..400 FORMULA a(n) = (1/4)*(3n-2)*(n-1)*(n-1)!. a(n) = (1/2)*(3n-4)*(n-1)! + (n-1)*a(n-1); a(1)=0. a(n) = (n+2)!*Sum_{k=1..n} ((2*k-1)/(k*(k+1)*(k+2))). - Gary Detlefs, Sep 20 2011 EXAMPLE a(2)=1 because the horizontal domino has no cells in the 2nd row and the vertical domino has 1 cell in the 2nd row. MAPLE seq((1/4)*(3*n-2)*(n-1)*factorial(n-1), n = 1 .. 18) MATHEMATICA Table[((3n-2)(n-1)(n-1)!)/4, {n, 20}] (* Harvey P. Dale, Sep 23 2011 *) PROG (MAGMA)[(3*n-2)*(n-1)*Factorial(n-1)/4: n in [1..20]]; // Vincenzo Librandi, Sep 24 2011 CROSSREFS Cf. A134436. Sequence in context: A301319 A143835 A103719 * A018927 A001266 A071971 Adjacent sequences:  A134434 A134435 A134436 * A134438 A134439 A134440 KEYWORD nonn AUTHOR Emeric Deutsch, Nov 30 2007 STATUS approved

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Last modified December 2 23:09 EST 2020. Contains 338898 sequences. (Running on oeis4.)