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%I
%S 0,1,1,7,13,19,31,43,55,73,85,109,121,151,169,199,235,253,295,313,361,
%T 397,433,475,511,571,595,661,703,757,817,859,925,979,1039,1111,1159,
%U 1237,1285,1381,1453,1519,1597,1663,1759,1813,1915,1993,2077,2173,2257
%N Open disk numbers (version 3): a(n) is the number of points (i+j/2,j*sqrt(3)/2), i,j integers (triangular grid) contained in an open disk of diameter n, centered at (0,0).
%C a(n)/(n/2)^2 --> Pi*2/sqrt(3).
%Y Cf. A053416, A053456, A053457, A053459.
%K easy,nonn
%O 0,4
%A Klaus Strassburger (strass(AT)ddfi.uni-duesseldorf.de), Jan 13 2000
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