A190640 Numbers whose base-3 expansion ends in 2 and does not contain any 1's.

2, 8, 20, 26, 56, 62, 74, 80, 164, 170, 182, 188, 218, 224, 236, 242, 488, 494, 506, 512, 542, 548, 560, 566, 650, 656, 668, 674, 704, 710, 722, 728, 1460, 1466, 1478, 1484, 1514, 1520, 1532, 1538, 1622, 1628, 1640, 1646, 1676, 1682, 1694, 1700, 1946, 1952, 1964, 1970, 2000, 2006, 2018, 2024, 2108, 2114, 2126

Offset: 1

Author

N. J. A. Sloane, May 15 2011

Keywords

• nonn
• base
• easy

Links

• Vincenzo Librandi, Table of n, a(n) for n = 1..1000

Crossrefs

Subsequence of A005823.

Cf. A005836.

Programs

Mathematica

Select[Range[2200],Last[IntegerDigits[#,3]]==2&&DigitCount[#,3,1]==0&] (* Harvey P. Dale, Sep 09 2012 *)
FromDigits[#,3]&/@(Join[#,{2}]&/@Tuples[{0,2},7]) (* Harvey P. Dale, Jul 25 2020 *)

PARI

is(n)=n%3==2 && setsearch(Set(digits(n,3)), 1)==0 \\ Charles R Greathouse IV, Aug 24 2016

PARI

a(n)=2*fromdigits(binary(2*n-1),3) \\ Charles R Greathouse IV, Aug 24 2016

Formula

Conjecture: a(n) = A055246(n) + 1. - Michel Marcus, Aug 24 2016

a(n) = A005823(2n). - Charles R Greathouse IV, Aug 24 2016