A233919 a(n) is the number of noncomposites (primes or 1) that are n digits long in balanced ternary notation.

1, 2, 4, 6, 18, 42, 111, 279, 752, 1990, 5376, 14707, 40465, 111970, 311997, 873239, 2455818, 6933060, 19640273, 55813426, 159047591, 454373344, 1301016216, 3733009232, 10731465131, 30904208376, 89140202911, 257498974953, 744861243809, 2157405104355

Offset: 1

Author

Lei Zhou, Dec 17 2013

Keywords

• nonn
• base

Crossrefs

Cf. A004676, A162145.

Programs

Mathematica

BTSeg[d_Integer] := Module[{}, {3^d - (3^d - 1)/2, 3^d + (3^d - 1)/2}];
Table[s = BTSeg[d]; PrimePi[Ceiling[s[[2]]/2]*2] - PrimePi[s[[1]] - 1], {d, 0, 29}]