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Smallest k such that 2^k has exactly n 6's in its decimal representation.
9

%I #13 Jun 26 2018 05:03:00

%S 1,4,16,36,60,100,72,123,124,161,157,243,196,230,222,220,300,323,361,

%T 447,378,551,433,506,555,565,636,508,606,662,701,778,810,746,823,839,

%U 850,977,1074,861,1046,1086,996,1161,1067,1168,1083,983,1223,1252,1303

%N Smallest k such that 2^k has exactly n 6's in its decimal representation.

%H Harry J. Smith, <a href="/A063540/b063540.txt">Table of n, a(n) for n = 0..150</a>

%t a = {}; Do[k = 1; While[ Count[ IntegerDigits[2^k], 6] != n, k++ ]; a = Append[a, k], {n, 0, 50} ]; a

%o (PARI) a(n)={my(k=1); while(n<>#select(d->d==6, digits(2^k)), k++); k} \\ _Harry J. Smith_, Aug 25 2009, _Andrew Howroyd_, Jun 26 2018

%Y Cf. A063115, A063426, A063429, A063430, A063526, A063552, A063553, A063554.

%K base,nonn

%O 0,2

%A _Robert G. Wilson v_, Aug 10 2001

%E Name corrected by _Jon E. Schoenfield_, Jun 25 2018