A131544 - OEIS

%I #18 Mar 20 2019 19:11:32

%S 2,34,35,276,1520,2342,8882,32313,164065,265693,1123487,2421341,

%T 6250773,9995032,68353789,78927182

%N Least power of 3 having exactly n consecutive 9's in its decimal representation.

%C No more terms < 10^8. - _Bert Dobbelaere_, Mar 20 2019

%e 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 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 (Python)

%o def A131544(n):

%o ....m, s = 1, '9'*n

%o ....for i in range(1,10**9):

%o ........m *= 3

%o ........if s in str(m):

%o ............return i

%o ....return "search limit reached." # _Chai Wah Wu_, Dec 11 2014

%Y Cf. A195269, A131552, A131551, A131550, A131549, A131548, A131547, A131546, A131545.

%K more,nonn,base

%O 1,1

%A _Shyam Sunder Gupta_, Aug 26 2007

%E a(11)-a(14) from _Lars Blomberg_, Feb 02 2013

%E a(15) from _Bert Dobbelaere_, Mar 04 2019

%E a(16) from _Bert Dobbelaere_, Mar 20 2019