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%I #15 Jul 30 2023 13:41:35
%S 1,5,49,25,35,109,96,128,135,169,182,156,208,302,310,277,221,300,346,
%T 498,387,502,563,507,503,611,550,585,615,681,731,817,819,835,779,860,
%U 849,840,879,997,1016,925,1066,1161,1117,1186,1282,1090,1293,1251,1444
%N Smallest k such that 2^k has exactly n 3's in its decimal representation.
%H Harry J. Smith, <a href="/A063429/b063429.txt">Table of n, a(n) for n = 0..150</a>
%t a = {}; Do[k = 1; While[ Count[ IntegerDigits[2^k], 3] != n, k++ ]; a = Append[a, k], {n, 0, 50} ]; a
%t With[{dr=Table[{k,DigitCount[2^k,10,3]},{k,1500}]},Table[SelectFirst[dr,#[[2]]==n&],{n,0,50}]][[;;,1]] (* _Harvey P. Dale_, Jul 30 2023 *)
%o (PARI) a(n)={my(k=1); while(n<>#select(d->d==3, digits(2^k)), k++); k} \\ _Harry J. Smith_, Aug 20 2009, _Andrew Howroyd_, Jun 26 2018
%Y Cf. A063115, A063426, A063430, 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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