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%I #10 Feb 07 2016 21:40:42
%S 0,6,6,24,24,54,60,96,114,150,180,216,258,324,348,426,450,540,564,666,
%T 720,804,870,954,1056,1134,1230,1344,1416,1542,1614,1752,1842,1974,
%U 2100,2208,2346,2478,2628,2778,2898,3084,3180,3378,3474,3684,3822,4002,4176,4356
%N Number of unit triangular lattice cells enclosed by origin centered circle of diameter n.
%C As n -> infinity, lim a(n)/(n^2) -> Pi/sqrt(3).
%H Luca Petrone, <a href="/A267710/b267710.txt">Table of n, a(n) for n = 1..200</a>
%Y Cf. A093602 (Pi/sqrt(3)).
%K easy,nonn
%O 1,2
%A _Luca Petrone_, Jan 19 2016