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 A131544 #22 Mar 20 2025 14:24:50
%S A131544 2,34,35,276,1520,2342,8882,32313,164065,265693,1123487,2421341,
%T A131544 6250773,9995032,68353789,78927182
%N A131544 Least power of 3 having exactly n consecutive 9's in its decimal representation.
%C A131544 No more terms < 10^8. - _Bert Dobbelaere_, Mar 20 2019
%e A131544 a(3)=35 because 3^35 (i.e., 50031545098999707) is the smallest power of 3 to contain a run of 3 consecutive nines in its decimal form.
%t A131544 a = ""; Do[ a = StringJoin[a, "9"]; b = StringJoin[a, "9"]; k = 1; While[ StringPosition[ ToString[3^k], a] == {} || StringPosition[ ToString[3^k], b] != {}, k++ ]; Print[k], {n, 1, 10} ]
%o A131544 (Python)
%o A131544 def A131544(n):
%o A131544 m, s = 1, '9'*n
%o A131544 for i in range(1,10**9):
%o A131544 m *= 3
%o A131544 if s in str(m):
%o A131544 return i
%o A131544 return "search limit reached." # _Chai Wah Wu_, Dec 11 2014
%Y A131544 Cf. A195269, A131552, A131551, A131550, A131549, A131548, A131547, A131546, A131545.
%K A131544 more,nonn,base
%O A131544 1,1
%A A131544 _Shyam Sunder Gupta_, Aug 26 2007
%E A131544 a(11)-a(14) from _Lars Blomberg_, Feb 02 2013
%E A131544 a(15) from _Bert Dobbelaere_, Mar 04 2019
%E A131544 a(16) from _Bert Dobbelaere_, Mar 20 2019