%I #25 Jan 01 2016 17:28:58

%S 1,1,1,2,2,2,3,3,3,2,2,2,4,5,5,5,2,6,6,5,5,1,1,8,8,4,9,9,3,8,10,10,10,

%T 11,11,11,12,4,12,11,8,1,1,5,5,12,12,3,15,7,16,3,3,7,8,8,8,12,7,7,10,

%U 1,1,7,4,4,21,13,7,4,4,22,6,6,4,23,24,13,2,4,25,1,1,11,6,26,3,2,12,12,12,11,14,14,23,3,3,4,4,4,3,1,1,2,2,2,6,6,8,2,2,2,3,3,3,17,2,5,6,6,6

%N Position of rightmost zero in 2^n (including leading zero).

%C "Positions" are counted 0,1,2,3,... starting with the least significant digit.

%H Alois P. Heinz, <a href="/A181611/b181611.txt">Table of n, a(n) for n = 1..10000</a>

%F a(n) = A215887(A000079(n)). - _Michel Marcus_, Jan 01 2016

%e 2^10 = 1024, the rightmost zero is in position 2, so a(10) = 2. Another example, 2^5 = 32, so we need to add a leading zero: 032, thus the rightmost zero will be in position 2, and a(5) = 2.

%p A181611 := proc(n) local dgs,i ; dgs := convert(2^n, base, 10) ; i := ListTools[Search](0, dgs) ; if i > 0 then i-1; else nops(dgs) ; end if ; end proc: # _R. J. Mathar_, Jan 30 2011

%p a:= proc(n) local m, i;

%p m:= 2^n;

%p for i from 0 while m>0 and irem(m, 10, 'm')<>0

%p do od; i

%p end:

%p seq(a(n), n=1..121); # _Alois P. Heinz_, Feb 05 2011

%t Table[Position[Reverse[Prepend[IntegerDigits[2^n], 0]],

%t 0][[1]][[1]] - 1, {n, 121}]

%o (PARI) a(n) = {my(d = Vecrev(digits(2^n))); for (i=1, #d, if (!d[i], return (i-1));); #d;} \\ _Michel Marcus_, Jan 01 2016

%Y Cf. A031142, A031141.

%Y Cf. A000079, A215887.

%K nonn,base

%O 1,4

%A _Tanya Khovanova_, Jan 30 2011