%I A055607
%S A055607 0,0,2,4,7,10,14,19,24,30,36,44,51,60,68,79,88,100,110,124,135,150,162,
%T A055607 179,192,210,224,244,259,280,296,319,336,360,378,404,423,450,470,499,
%U A055607 520,550,572,604,627,660,684,719,744,780,806,844,871,910,938,979,1008
%N A055607 a(2n+1) = n^2 - 1 + A002620(n), a(2n) = a(2n-1) + n.
%C A055607 Consider an n X n chessboard. Place n queens in the cells of the first 
               row, in cells (1,1), (2,1),..., (n,1) and [(n+1)/2] pawns in the 
               odd cells of the second row, namely in cells (1,2), (3,2), (5,2), 
               ... Which is the number of the unattacked (by the queens) cells ? 
               How many cells are not attacked by the queens?
%D A055607 Suggested by a chess-board problem from Antreas P. Hatzipolakis.
%F A055607 G.f. x^3(x^4-x^3-x^2-2x-2)/(x-1)^3/(x+1)^2/(x^2+1). - Ralf Stephan (ralf(AT)ark.in-berlin.de), 
               Jul 25 2003
%p A055607 f := [0,0]: for i from 3 by 2 to 60 do f := [op(f),((i-1)/2)^2 - 1 + 
               floor((i-1)/4)*ceil((i-1)/4)]: f := [op(f),f[nops(f)] + (i+1)/2]: 
               od: f;
%Y A055607 Sequence in context: A145106 A127723 A076268 this_sequence A024512 A047808 
               A007980
%Y A055607 Adjacent sequences: A055604 A055605 A055606 this_sequence A055608 A055609 
               A055610
%K A055607 nonn,easy
%O A055607 1,3
%A A055607 Leonard Smiley (smiley(AT)math.uaa.alaska.edu), Jun 02 2000
%E A055607 More terms from Asher Natan Auel (auela(AT)reed.edu)