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A122748 Bishops on an n X n board (see Robinson paper for details). 1
1, 1, 2, 2, 4, 8, 16, 40, 72, 260, 432, 1976, 2880, 17632, 23040, 177248, 201600, 2001680, 2016000, 24879520, 21772800, 338969216, 261273600, 5002865792, 3353011200, 79676972608, 46942156800, 1358997441920, 697426329600, 24740358817280, 11158821273600, 478218277674496 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,3

REFERENCES

R. W. Robinson, Counting arrangements of bishops, pp. 198-214 of Combinatorial Mathematics IV (Adelaide 1975), Lect. Notes Math., 560 (1976). (M_n, p. 208)

LINKS

Table of n, a(n) for n=0..31.

MAPLE

unprotect(D); D:=proc(n) option remember; if n <= 1 then 1 else D(n-1)+(n-1)*D(n-2); fi; end; # Gives A000085

M:=proc(n) local k; if n mod 2 = 0 then k:=n/2; if k mod 2 = 0 then RETURN( k!*(k+2)/2 ); else RETURN( (k-1)!*(k+1)^2/2 ); fi; else k:=(n-1)/2; RETURN(D(k)*D(k+1)); fi; end;

CROSSREFS

Sequence in context: A090129 A001137 A123593 * A108774 A063402 A175195

Adjacent sequences:  A122745 A122746 A122747 * A122749 A122750 A122751

KEYWORD

nonn

AUTHOR

N. J. A. Sloane, Sep 25 2006

STATUS

approved

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Last modified September 18 07:58 EDT 2019. Contains 327168 sequences. (Running on oeis4.)