%I #9 Jun 26 2018 19:10:14

%S 1,2,13,18,22,28,43,46,71,66,83,104,86,128,127,125,139,142,124,190,

%T 195,185,202,216,215,265,235,245,244,263,278,282,274,277,286,310,320,

%U 323,432,348,376,448,400,392,459,446,441,413,587,456,486

%N Smallest k such that 7^k has exactly n 9's in its decimal representation.

%t a = {}; Do[k = 1; While[ Count[ IntegerDigits[7^k], 9] != n, k++ ]; a = Append[a, k], {n, 0, 50} ]; a

%t With[{sev=Table[DigitCount[7^n,10,9],{n,600}]},Table[Position[sev,i,{1},1],{i,0,50}]]//Flatten (* _Harvey P. Dale_, May 04 2016 *)

%K base,nonn

%O 0,2

%A _Robert G. Wilson v_, Aug 10 2001

%E Name corrected by _Jon E. Schoenfield_, Jun 26 2018