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%I #16 Jul 31 2013 04:18:09
%S 2,4,6,8,9,11,13,15,18,20,22,24,25,27,29,31,34,36,38,40,41,43,45,47,
%T 50,52,54,56,57,59,61,63
%N The squares on a chessboard that are black, counting from top left corner and down.
%C Equivalently it represents the squares that are white, counting from bottom left corner and up.
%F a(1) = 2
%F a(n) = a(n-1) + 2 + (mod(a(n-1)+1, 8) == 0) - (mod(a(n-1), 8) == 0)
%t sqColor[n_] := Mod[n, 2] + (1 - 2*Mod[n, 2])*Mod[Floor[(n - 1)/8], 2]; Select[Range[64], sqColor[#] == 0 &]
%Y Cf. A225240 (white-squares sequence).
%K nonn,easy,fini,full
%O 1,1
%A _Jonas Hallgren_, Jul 26 2013