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

1,2

Links

Table of n, a(n) for n=1..30.

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}]

Crossrefs

Cf. A004676, A162145.

Sequence in context: A023149 A085146 A066894 * A111115 A195328 A294447

Adjacent sequences: A233916 A233917 A233918 * A233920 A233921 A233922

Keyword

nonn,base

Author

Lei Zhou, Dec 17 2013

Status

approved