Search: id:A037223 Results 1-1 of 1 results found. %I A037223 %S A037223 1,1,2,2,8,8,48,48,384,384,3840,3840,46080,46080,645120,645120,10321920, %T A037223 10321920,185794560,185794560,3715891200,3715891200,81749606400, %U A037223 81749606400,1961990553600,1961990553600,51011754393600,51011754393600 %N A037223 Number of solutions to non-attacking rooks problem on n X n board that are invariant under 180 degree rotation. %C A037223 This is just A000165 doubled up. Normally such sequences do not get their own entry in the OEIS. This is an exception. - N. J. A. Sloane (njas(AT)research.att.com), Sep 23 2006 %C A037223 Also the number of permutations of (1,2,3,...,n) for which the reverse of the inverse is the same as the inverse of the reverse. - Ian Duff (ianfduff(AT)yahoo.co.uk), Mar 09 2007 %D A037223 E. Lucas, Theorie des nombres, Gauthiers-Villars, Paris, 1891, Vol 1, p. 221. %D A037223 R. W. Robinson, Counting arrangements of bishops, pp. 198-214 of Combinatorial Mathematics IV (Adelaide 1975), Lect. Notes Math., 560 (1976). %H A037223 M. Szabo, Non-attacking Queens Problem Page %F A037223 a(2n) = a(2n+1) = (n)!*2^(n). %F A037223 Exponential generating function: 1+x+(1+x+x^2)*exp(x^2/2)*sqrt(Pi/2)*erf(x/ sqrt(2)), where erf denotes the error function. - Antonio G. Astudillo (afg_astudillo(AT)hotmail.com), Nov 01 2002 %F A037223 For asymptotics see the Robinson paper. %p A037223 For Maple program see A000903. %Y A037223 Cf. A000165, A033148, A037224, A032522, A037223. %Y A037223 Sequence in context: A007083 A144060 A016119 this_sequence A066988 A100384 A000023 %Y A037223 Adjacent sequences: A037220 A037221 A037222 this_sequence A037224 A037225 A037226 %K A037223 nonn %O A037223 0,3 %A A037223 Miklos SZABO (mike(AT)ludens.elte.hu) %E A037223 More terms from Antonio G. Astudillo (afg_astudillo(AT)hotmail.com), Nov 01 2002 %E A037223 Edited by N. J. A. Sloane (njas(AT)research.att.com), Sep 23 2006 Search completed in 0.002 seconds