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%I #14 Jun 26 2018 05:00:55
%S 1,2,18,22,64,91,117,111,164,138,182,233,219,253,343,266,264,321,315,
%T 331,450,349,451,469,553,504,510,687,592,630,710,744,808,767,828,889,
%U 722,951,789,942,918,964,1066,1033,890,1183,1263,1171,1229,1130,1291
%N Smallest k such that 2^k has exactly n 4's in its decimal representation.
%H Harry J. Smith, <a href="/A063430/b063430.txt">Table of n, a(n) for n = 0..150</a>
%t a = {}; Do[k = 1; While[ Count[ IntegerDigits[2^k], 4] != n, k++ ]; a = Append[a, k], {n, 0, 50} ]; a
%o (PARI) a(n)={my(k=1); while(n<>#select(d->d==4, digits(2^k)), k++); k} \\ _Harry J. Smith_, Aug 20 2009, _Andrew Howroyd_, Jun 26 2018
%Y Cf. A063115, A063426, A063429, A063526, A063540, 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
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