

A006889


Exponent of least power of 2 having n consecutive 0's in its decimal representation.
(Formerly M4710)


14



0, 10, 53, 242, 377, 1491, 1492, 6801, 14007, 100823, 559940, 1148303, 4036338, 4036339, 53619497, 119476156, 146226201, 918583174, 4627233991, 11089076233
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OFFSET

0,2


COMMENTS

A224782(a(n)) = n and A224782(m) <> n for m < a(n).  Reinhard Zumkeller, Apr 30 2013
The name of this sequence previously began "Least power of 2 having exactly n consecutive 0's...". The word "exactly" was unnecessary because the least power of 2 having at least n consecutive 0's in its decimal representation will always have exactly n consecutive 0's. The previous power of two will have had n1 consecutive 0's with a "5" immediately to the left.  Clive Tooth, Jan 22 2016
a(20) is greater than 12*10^9.  Benjamin Chaffin, Jan 18 2017


REFERENCES

Julian Havil, Impossible?: Surprising Solutions to Counterintuitive Conundrums, Princeton University Press 2008, chapter 15, p. 176ff
Popular Computing (Calabasas, CA), Zeros in Powers of 2, Vol. 3 (No. 25, Apr 1975), page PC2516 [Gives a(1)a(8)]
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).


LINKS

Table of n, a(n) for n=0..19.
E. Karst and U. Karst, The first power of 2 with 8 consecutive zeros, Math. Comp. 18 (1964), 508508.
Popular Computing (Calabasas, CA), Two Tables, Vol. 1, (No. 9, Dec 1973), page PC916.


EXAMPLE

2^53619497 is the smallest power of 2 to contain a run of 14 consecutive zeros in its decimal form.
2^119476156 (a 35965907digit number) contains the sequence ...40030000000000000008341... about one third of the way through.
2^4627233991 (a 1392936229digit number) contains the sequence "813000000000000000000538" about 99.5% of the way through. The computation took about six months.


MAPLE

A[0]:= 0:
m:= 1:
for n from 1 while m <= 9 do
S:= convert(2^n, string);
if StringTools:Search(StringTools:Fill("0", m), S) <> 0 then
A[m]:= n;
m:= m+1;
fi
od:
seq(A[i], i=0..9); # Robert Israel, Jan 22 2016


MATHEMATICA

a = ""; Do[ a = StringJoin[a, "0"]; k = 1; While[ StringPosition[ ToString[2^k], a] == {}, k++ ]; Print[k], {n, 1, 10} ] (* Robert G. Wilson v, edited by Clive Tooth, Jan 25 2016 *)


PROG

(Haskell)
import Data.List (elemIndex)
import Data.Maybe (fromJust)
a006889 = fromJust . (`elemIndex` a224782_list)
 Reinhard Zumkeller, Apr 30 2013
(PARI) conseczerorec(n) = my(d=digits(n), i=0, r=0, x=#Str(n)); while(x > 0, while(d[x]==0, i++; x); if(i > r, r=i); i=0; x); r
a(n) = my(k=0); while(conseczerorec(2^k) < n, k++); k \\ Felix Fröhlich, Sep 27 2016


CROSSREFS

Cf. A031146.
Cf. also A131535, A131536, A259089, A063565, A259091, A259092.
Sequence in context: A216938 A298564 A063899 * A300422 A300684 A300607
Adjacent sequences: A006886 A006887 A006888 * A006890 A006891 A006892


KEYWORD

nonn,hard,base,more,changed


AUTHOR

P. D. Mitchelmore (dh115(AT)city.ac.uk)


EXTENSIONS

3 more terms from Clive Tooth, Jan 24 2001
One more term from Clive Tooth, Nov 28 2001
One more term from Sacha Roscoe (scarletmanuka(AT)iprimus.com.au), Dec 16 2002
a(17) from Sacha Roscoe (scarletmanuka(AT)iprimus.com.au), Feb 06 2007
a(18) from Clive Tooth, Sep 30 2012
Name clarified by Clive Tooth, Jan 22 2016
Definition clarified by Felix Fröhlich, Sep 27 2016
a(19) from Benjamin Chaffin, Jan 18 2017


STATUS

approved



