%I #29 Jan 27 2021 05:34:44
%S 1,8,11,18,21,28,31,38,41,48,51,58,61,68,71,81,91,101,104,111,114,121,
%T 124,131,134,141,144,151,154,161,164,171,174,184,194,197,204,207,214,
%U 217,224,227,234,237,244,247,254,257,264,267,277,287,297,300,307,310
%N Numbers k such that 2 is the first digit of 2^k.
%C The asymptotic density of this sequence is log_10(3/2) = 0.176091... (A154580 - 1). - _Amiram Eldar_, Jan 27 2021
%H Muniru A Asiru, <a href="/A067469/b067469.txt">Table of n, a(n) for n = 1..5000</a>
%t Select[Range@ 310, First@ IntegerDigits[2^#] == 2 &] (* _Michael De Vlieger_, Oct 15 2018 *)
%o (PARI) is(n)=digits(2^n)[1]==2 \\ _Charles R Greathouse IV_, Jul 29 2013
%o (GAP) Filtered([1..310],n->ListOfDigits(2^n)[1]=2); # _Muniru A Asiru_, Oct 14 2018
%Y Cf. A067480, A154580.
%K nonn,base
%O 1,2
%A _Benoit Cloitre_, Feb 22 2002