This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A030439 #18 Jul 08 2025 19:33:13 %S A030439 0,1,2,3,8,9,26,27,80,81,242,243,728,729,2186,2187,6560,6561,19682, %T A030439 19683,59048,59049,177146,177147,531440,531441,1594322,1594323, %U A030439 4782968,4782969,14348906,14348907,43046720,43046721,129140162,129140163,387420488,387420489 %N A030439 a(n+1) = smallest number not containing any digits of a(n), working in base 3. %H A030439 <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0, 4, 0, -3). %F A030439 3^i-1 then 3^i. %F A030439 a(n) = 4*a(n-2)-3*a(n-4); g.f.: -x*(x^2-2*x-1) / ((x-1)*(x+1)*(3*x^2-1)). - _Colin Barker_, Sep 13 2014 %F A030439 a(n) = 3^floor(n/2) -1 +(n mod 2). - _Alois P. Heinz_, Sep 14 2014 %Y A030439 Cf. A030283. %Y A030439 Bisections give: A024023, A000244. %K A030439 nonn,base %O A030439 0,3 %A A030439 _N. J. A. Sloane_