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Search: id:A131541
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| A131541 |
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Least power of 2 having exactly n consecutive 7's in its decimal representation. |
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+0
1
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| 15, 27, 24, 181, 317, 2309, 972, 25264, 131979, 279275
(list; graph; listen)
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OFFSET
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1,1
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EXAMPLE
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a(3)=24 because 2^24(i.e. 16777216) is the smallest power of 2 to contain a run of 3 consecutive sevens in its decimal form.
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MATHEMATICA
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a = ""; Do[ a = StringJoin[a, "7"]; b = StringJoin[a, "7"]; k = 1; While[ StringPosition[ ToString[2^k], a] == {} || StringPosition[ ToString[2^k], b] != {}, k++ ]; Print[k], {n, 1, 10} ]
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CROSSREFS
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Sequence in context: A063936 A132452 A063552 this_sequence A080945 A080946 A110703
Adjacent sequences: A131538 A131539 A131540 this_sequence A131542 A131543 A131544
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KEYWORD
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more,nonn,base
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AUTHOR
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Shyam Sunder Gupta (guptass(AT)rediffmail.com), Aug 26 2007
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