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 A122693 Bishops on an n X n board (see Robinson paper for details). 1
 0, 2, 4, 32, 128, 1152, 6912, 73728, 589824, 7372800, 73728000, 1061683200, 12740198400, 208089907200, 2913258700800, 53271016243200, 852336259891200, 17259809262796800, 310676566730342400, 6903923705118720000, 138078474102374400000, 3341499073277460480000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 REFERENCES R. W. Robinson, Counting arrangements of bishops, pp. 198-214 of Combinatorial Mathematics IV (Adelaide 1975), Lect. Notes Math., 560 (1976). (C_{2n+1}, Eq. (20)) LINKS Table of n, a(n) for n=0..21. R. W. Robinson, Counting arrangements of bishops, pp. 198-214 of Combinatorial Mathematics IV (Adelaide 1975), Lect. Notes Math., 560 (1976). (Annotated scanned copy) MAPLE C:=proc(n) local k; if n mod 2 = 0 then RETURN(0); fi; k:=(n-1)/2; if k mod 2 = 0 then RETURN( k*2^(k-1)*((k/2)!)^2 ); else RETURN( 2^k*(((k+1)/2)!)^2 ); fi; end; [seq(C(2*n+1), n=0..30)]; MATHEMATICA c[n_] := Module[{k}, If[Mod[n, 2] == 0, 0, k = (n-1)/2; If[Mod[k, 2] == 0, k*2^(k-1)*((k/2)!)^2, 2^k*(((k+1)/2)!)^2]]]; a[n_] := c[2n+1]; Table[a[n], {n, 0, 30}] (* Jean-François Alcover, Jul 23 2022, after Maple code *) CROSSREFS Sequence in context: A192387 A320624 A133127 * A019060 A247014 A085055 Adjacent sequences: A122690 A122691 A122692 * A122694 A122695 A122696 KEYWORD nonn AUTHOR N. J. A. Sloane, Sep 25 2006 STATUS approved

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Last modified September 23 14:27 EDT 2023. Contains 365551 sequences. (Running on oeis4.)