This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A181610 #18 Mar 21 2015 10:48:13
%S A181610 4,18,81,364,1638,7371,33170,149268,671701,3022653,13601945,61208743,
%T A181610 275439346,1239477074,5577646830,25099410745,112947348510,
%U A181610 508263067945,2287183805359,10292327123878,46315472056678,208419624257654,937888309161430,4220497391215744
%N A181610 The last n digits of powers of 2 start cycling. a(n) is the number of zero-free terms in this cycle.
%H A181610 Hiroaki Yamanouchi, <a href="/A181610/b181610.txt">Table of n, a(n) for n = 1..26</a>
%e A181610 The last two digits of powers of two cycle through 20 terms (A000855): 04, 08, 16, 32, 64, 28, 56, 12, 24, 48, 96, 92, 84, 68, 36, 72, 44, 88, 76, 52. Out of those 18 do not contain a zero. Hence a(2) = 18.
%t A181610 f[n_] := Block[{c = 0, k = n, lmt = n + 4*5^(n - 1)},
%t A181610 While[k < lmt, m = PowerMod[2, k, 10^n];
%t A181610 If[m >= 10^(n - 1) && !MemberQ[ IntegerDigits@ m, 0], c++ ]; k++ ]; c];
%t A181610 Array[ f, 11] (* _Robert G. Wilson v_, Jan 30 2011 *)
%Y A181610 The corresponding cycle length is A005054. See A126605 for n=3.
%K A181610 nonn,base
%O A181610 1,1
%A A181610 _Tanya Khovanova_, Jan 30 2011
%E A181610 a(8)-a(11) from _Robert G. Wilson v_, Jan 30 2011
%E A181610 a(12)-a(24) from _Hiroaki Yamanouchi_, Mar 21 2015