%I #6 Jun 26 2018 19:18:07

%S 1,10,15,12,23,60,58,76,83,85,114,130,151,141,180,107,174,190,249,187,

%T 248,220,212,269,287,297,237,316,327,370,405,383,416,313,424,412,390,

%U 483,512,496,479,502,596,578,626,581,612,593,446,587,600

%N Smallest k such that 4^k has exactly n 7's in its decimal representation.

%t a = {}; Do[k = 1; While[ Count[ IntegerDigits[4^k], 7] != n, k++ ]; a = Append[a, k], {n, 0, 50} ]; a

%K base,nonn

%O 0,2

%A _Robert G. Wilson v_, Aug 10 2001

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