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A233919 a(n) is the number of noncomposites (primes or 1) that are n digits long in balanced ternary notation. 0
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 (list; graph; refs; listen; history; text; internal format)
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

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Last modified August 12 16:40 EDT 2020. Contains 336439 sequences. (Running on oeis4.)