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A146087 a(n) = 3*A146085(n) - 1. 1

%I

%S 2,11,20,83,92,101,164,173,182,731,740,749,812,821,830,893,902,911,

%T 1460,1469,1478,1541,1550,1559,1622,1631,1640,6563,6572,6581,6644,

%U 6653,6662,6725,6734,6743,7292,7301,7310,7373,7382,7391,7454,7463,7472,8021,8030,8039,8102,8111,8120

%N a(n) = 3*A146085(n) - 1.

%C Positive integers such that for every integer m==8 (mod 9) there exists a unique representation of m as a sum of the form a(l)+3a(s).

%t fQ[n_] := Module[{d = Reverse[IntegerDigits[n, 3]], k = 3, ans = True}, While[k <= Length[d], If[d[[k]] > 0, ans = False]; k += 2]; ans && d[[1]] == 1]; aQ[n_] := Mod[n + 1, 3] == 0 && fQ[(n + 1)/3]; Select[Range[10000], aQ] (* _Amiram Eldar_, Dec 09 2018 *)

%o (PARI) isa(n) = {my(d=Vecrev(digits(n, 3)), k=3); while (k <= #d, if (d[k], return (0)); k += 2;); d[1] == 1;} \\ A146085

%o isok(n) = !((n+1) % 3) && isa((n+1)/3); \\ _Michel Marcus_, Dec 09 2018

%Y Cf. A146085, A145812, A145818.

%K nonn

%O 1,1

%A _Vladimir Shevelev_, Oct 27 2008

%E More terms from _Michel Marcus_, Dec 09 2018

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Last modified April 19 16:18 EDT 2019. Contains 322282 sequences. (Running on oeis4.)