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%I #6 Dec 08 2015 01:51:45
%S 1,2,4,6,18,42,111,279,752,1990,5376,14707,40465,111970,311997,873239,
%T 2455818,6933060,19640273,55813426,159047591,454373344,1301016216,
%U 3733009232,10731465131,30904208376,89140202911,257498974953,744861243809,2157405104355
%N a(n) is the number of noncomposites (primes or 1) that are n digits long in balanced ternary notation.
%t BTSeg[d_Integer] := Module[{}, {3^d - (3^d - 1)/2, 3^d + (3^d - 1)/2}];
%t Table[s = BTSeg[d]; PrimePi[Ceiling[s[[2]]/2]*2] - PrimePi[s[[1]] - 1], {d, 0, 29}]
%Y Cf. A004676, A162145.
%K nonn,base
%O 1,2
%A _Lei Zhou_, Dec 17 2013
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