%I A122747
%S A122747 1,4,144,14400,2822400,914457600,442597478400,299195895398400,269276305858560000,
%T A122747 311283409572495360000,449493243422683299840000,792906081397613340917760000,
%U A122747 1677789268237349829381980160000,4194473170593374573454950400000000,12231083765450280256194635366400000000
%N A122747 Bishops on an n X n board (see Robinson paper for details).
%C A122747 a(n) appears as coefficient of x^(2*n)/n! in the expansion of 1/sqrt(1-4*x^2). 
               [From Wolfdieter Lang (wolfdieter.lang(AT)physik.uni-karlsruhe.de), 
               Oct 06 2008]
%D A122747 R. W. Robinson, Counting arrangements of bishops, pp. 198-214 of Combinatorial 
               Mathematics IV (Adelaide 1975), Lect. Notes Math., 560 (1976). (Q_{8n+1}, 
               Eq. (22))
%e A122747 a(n)= ((2*n)!/n!)^2 = A001813(n)^2. [From Wolfdieter Lang (wolfdieter.lang(AT)physik.uni-karlsruhe.de), 
               Oct 06 2008]
%p A122747 Q:=proc(n) local m; if n mod 8 <> 1 then RETURN(0); fi; m:=(n-1)/8; ((2*m)!)^2/
               (m!)^2; end;
%Y A122747 Sequence in context: A036511 A060870 A084703 this_sequence A069135 A138176 
               A055209
%Y A122747 Adjacent sequences: A122744 A122745 A122746 this_sequence A122748 A122749 
               A122750
%K A122747 nonn
%O A122747 0,2
%A A122747 N. J. A. Sloane (njas(AT)research.att.com), Sep 25 2006