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Search: id:A016121
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| A016121 |
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Number of sequences (a_1, a_2, ..., a_n) of length n with a_1 = 1 satisfying a_i <= a_{i+1} <= 2*a_i. |
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13
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| 1, 2, 5, 17, 86, 698, 9551, 226592, 9471845, 705154187, 94285792211, 22807963405043, 10047909839840456, 8110620438438750647, 12062839548612627177590
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OFFSET
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0,2
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COMMENT
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Number of n X n binary symmetric matrices with rows, considered as binary numbers, in nondecreasing order. - Ron Hardin (rhhardin(AT)att.net), May 30 2008
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FORMULA
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a(n) = Sum_{k=0..n} A097712(n, k). - Paul D. Hanna (pauldhanna(AT)juno.com), Aug 24 2004
Equals the binomial transform of A008934 (number of tournament sequences): a(n) = Sum_{k=0..n} C(n, k)*A008934(k). - Paul D. Hanna (pauldhanna(AT)juno.com), Sep 18 2005
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CROSSREFS
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Row sums of triangle A097712.
Cf. A008934, A060690, A089006.
Sequence in context: A162041 A162042 A162043 this_sequence A026822 A059248 A143878
Adjacent sequences: A016118 A016119 A016120 this_sequence A016122 A016123 A016124
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KEYWORD
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nonn
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AUTHOR
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Jeffrey Shallit (shallit(AT)graceland.uwaterloo.ca)
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