A032819 - OEIS

%I #23 Sep 08 2022 08:44:51

%S 1,4,8,11,29,32,57,60,78,81,204,207,225,228,400,403,421,424,547,550,

%T 568,571,1429,1432,1450,1453,1576,1579,1597,1600,2801,2804,2822,2825,

%U 2948,2951,2969,2972,3830,3833,3851,3854,3977,3980

%N Numbers whose set of base-7 digits is {1,4}.

%H Vincenzo Librandi, <a href="/A032819/b032819.txt">Table of n, a(n) for n = 1..1000</a>

%H <a href="/index/Ar#7-automatic">Index entries for 7-automatic sequences</a>.

%F a(1)=1, a(2)=4; a(n) = 7*a(floor(n/2))+1 for n odd, otherwise a(n) = 7*a(floor((n-1)/2))+4. - _Bruno Berselli_, May 28 2012

%t Select[Range[4000],MemberQ[{{1},{4},{1,4}},Union[IntegerDigits[ #,7]]]&]  (* _Harvey P. Dale_, Apr 04 2011 *)

%t Flatten[Table[FromDigits[#,7]&/@Tuples[{1,4},n],{n,5}]] (* _Vincenzo Librandi_, May 28 2012 *)

%o (Magma) [n: n in [1..4000] | Set(IntegerToSequence(n, 7)) subset {1, 4}]; // _Vincenzo Librandi_, May 28 2012

%o (Maxima) a[1]:1$ a[2]:4$ a[n]:= if oddp(n) then 7*a[floor(n/2)]+1 else 7*a[floor((n-1)/2)]+4$ makelist(a[n],n,1,44); /* _Bruno Berselli_, May 28 2012 */

%K nonn,base,easy

%O 1,2

%A _Clark Kimberling_