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Search: id:A078221
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| A078221 |
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a(1) = 1, a(n+1) > a(n) is the smallest multiple of a(n) using only odd digits. |
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+0
9
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| 1, 3, 9, 99, 9999, 99999999, 9999999999999999, 99999999999999999999999999999999, 9999999999999999999999999999999999999999999999999999999999999999
(list; graph; listen)
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OFFSET
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1,2
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FORMULA
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a(n)=10^(2^(n-3))-1 for n >= 3. (Proof by induction. Consider a(n)*f, l=ceil(log(f)/log(10)), g1=number formed by the first l digits of a(n)*f, g2=number formed by the last l digits of a(n)*f => g1+g2=number formed by l 9's, if l<=10^(2^(n-2))+1) - Sascha Kurz (sascha.kurz(AT)uni-bayreuth.de), Jan 04 2003
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MAPLE
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1, 3, seq(10^(2^(n-3))-1, n=3..11);
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CROSSREFS
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Cf. A078222.
Adjacent sequences: A078218 A078219 A078220 this_sequence A078222 A078223 A078224
Sequence in context: A003225 A007663 A018695 this_sequence A018716 A018725 A135989
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KEYWORD
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base,nonn
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AUTHOR
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Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Nov 22 2002
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EXTENSIONS
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More terms from Sascha Kurz (sascha.kurz(AT)uni-bayreuth.de), Jan 04 2003
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