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Numbers n such that 3 is the first digit of 3^n.
3

%I #20 Dec 11 2020 19:23:31

%S 1,18,20,22,41,43,62,64,66,83,85,87,106,108,110,127,129,131,150,152,

%T 171,173,175,194,196,215,217,219,236,238,240,259,261,263,280,282,284,

%U 303,305,324,326,328,347,349,368,370,372,389,391,393,412,414,416,433

%N Numbers n such that 3 is the first digit of 3^n.

%H Vincenzo Librandi, <a href="/A054565/b054565.txt">Table of n, a(n) for n = 1..1000</a>

%t Select[Range[500],First[IntegerDigits[3^#]]==3&] (* _Harvey P. Dale_, Dec 23 2012 *)

%o (PARI) for(n=1,100, if(floor(3^n/10^(floor(n*log(3)/log(10))))==3,print1(n,",")))

%Y Cf. A067481.

%K nonn,base

%O 1,2

%A _Benoit Cloitre_, Feb 22 2002

%E Corrected by _T. D. Noe_, Nov 01 2006

%E Corrected by _Harvey P. Dale_, Dec 23 2012