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Search: id:A160393
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| 1, 2, 4, 7, 11, 20, 34, 58, 100, 172, 298, 516, 893, 1547, 2679, 4640, 8036, 13918, 24107, 41754, 72320, 125262, 216960, 375786
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OFFSET
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1,2
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COMMENT
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This sequence gives a lower bound for A090246. A003462 is the number of points in P(Z/3Z)^n. If a subset of P(Z/3Z)^n contains m points with no 3 colinear, then there are at most 2*C(m,2) points which are colinear with 2 points of the subset. Therefore if m + 2*C(m,2) = m^2 < A003462(n) we can add at least one more point to the set.
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FORMULA
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a(n)=ceil(sqrt((3^n-1)/2))
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CROSSREFS
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Cf. A090246, A003462
Sequence in context: A080005 A151992 A024501 this_sequence A018173 A146156 A024927
Adjacent sequences: A160390 A160391 A160392 this_sequence A160394 A160395 A160396
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KEYWORD
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easy,nonn
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AUTHOR
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Jack Grahl (jgrahl(AT)math.ucl.ac.uk), May 12 2009
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