A278997 Numbers of the form (3h+2)*3^(2k)-1 or (3h+1)*3^(2k+1)-1 for h,k in N.

1, 2, 4, 7, 10, 11, 13, 16, 17, 19, 20, 22, 25, 26, 28, 29, 31, 34, 37, 38, 40, 43, 44, 46, 47, 49, 52, 55, 56, 58, 61, 64, 65, 67, 70, 71, 73, 74, 76, 79, 82, 83, 85, 88, 91, 92, 94, 97, 98, 100, 101, 103, 106, 107, 109, 110, 112, 115, 118, 119, 121, 124, 125, 127, 128, 130

Offset: 1

Author

N. J. A. Sloane, Dec 07 2016

Keywords

• nonn

Comments

n is in the sequence if and only if either n == 1, 2, 4, or 7 (mod 9) or n == 8 (mod 9) and (n-8)/9 is in the sequence. - Robert Israel, Dec 18 2016

Links

• Ray Chandler, Table of n, a(n) for n = 1..10000
• Hao Fu and G.-N. Han, Computer assisted proof for Apwenian sequences related to Hankel determinants, arXiv preprint arXiv:1601.04370 [math.NT], 2016. See sequence "K" in Section 2.1.

Crossrefs

Complement of A278996.

Positions of 1's in A156595.

Programs

Maple

filter:= proc(n) local m;
  m:= padic:-ordp(n+1,3);
  (n+1)/3^m mod 3 = 2 - (m mod 2)
end proc:
select(filter, [$0..100]); # Robert Israel, Dec 18 2016

Mathematica

isok[n_]:=Module[{ord=IntegerExponent[n+1,3]},Mod[(n+1)/3^ord,3]!=Mod[ord,2]+1];Select[Range[0,100],isok](* Ray Chandler, Dec 17 2016 *)

Extensions

More terms from Ray Chandler, Dec 17 2016