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%I #10 Jun 26 2018 19:17:21
%S 1,6,17,16,45,56,46,70,77,86,93,122,127,173,171,166,172,214,178,217,
%T 253,300,265,238,286,266,298,364,331,343,368,365,446,447,425,423,396,
%U 483,480,506,576,575,594,592,678,579,671,621,539,664,620
%N Smallest k such that 4^k has exactly n 9's in its decimal representation.
%t a = {}; Do[k = 1; While[ Count[ IntegerDigits[4^k], 9] != n, k++ ]; a = Append[a, k], {n, 0, 50} ]; a
%t With[{n9s=DigitCount[#,10,9]&/@(4^Range[700])},Flatten[Table[ Position[ n9s,n,{1},1],{n,0,50}]]] (* _Harvey P. Dale_, Oct 20 2013 *)
%K base,nonn
%O 0,2
%A _Robert G. Wilson v_, Aug 10 2001
%E Name corrected by _Jon E. Schoenfield_, Jun 26 2018
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