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A131539
Exponent of least power of 2 having exactly n consecutive 5's in its decimal representation.
2
0, 8, 16, 76, 41, 1162, 973, 6838, 25265, 81782, 456686, 279270, 1727606, 6030753, 23157026, 106892455
OFFSET
0,2
LINKS
Popular Computing (Calabasas, CA), Two Tables, Vol. 1, (No. 9, Dec 1973), page PC9-16.
EXAMPLE
a(3)=76 because 2^76 (i.e., 75557863725914323419136) is the smallest power of 2 to contain a run of 3 consecutive fives in its decimal form.
MATHEMATICA
a = ""; Do[ a = StringJoin[a, "5"]; b = StringJoin[a, "5"]; k = 1; While[ StringPosition[ ToString[2^k], a] == {} || StringPosition[ ToString[2^k], b] != {}, k++ ]; Print[k], {n, 1, 10} ]
CROSSREFS
Sequence in context: A278747 A218066 A157164 * A331419 A271080 A117868
KEYWORD
more,nonn,base
AUTHOR
Shyam Sunder Gupta, Aug 26 2007
EXTENSIONS
2 more terms from Sean A. Irvine, Jul 19 2010
a(13)-a(14) from Lars Blomberg, Jan 24 2013
a(0)=0 prepended by and a(15) from Paul Geneau de Lamarlière, Jul 19 2024
STATUS
approved