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Search: id:A015552
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| A015552 |
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Linear 2nd order recurrence. |
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+0
2
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| 0, 1, 6, 43, 300, 2101, 14706, 102943, 720600, 5044201, 35309406, 247165843, 1730160900, 12111126301, 84777884106, 593445188743, 4154116321200, 29078814248401, 203551699738806, 1424861898171643, 9974033287201500
(list; graph; listen)
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OFFSET
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0,3
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COMMENT
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Number of walks of length n between any two distinct nodes of the complete graph K_8. Example: a(2)=6 because the walks of length 2 between the nodes A and B of the complete graph ABCDEFGH are: ACB, ADB, AEB, AFB, AGB, and AHB. - Emeric Deutsch (deutsch(AT)duke.poly.edu), Apr 01 2004
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FORMULA
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a(n) = 6 a(n-1) + 7 a(n-2).
G.f.: x/(1-6x-7x^2). a(n)=7^(n-1)-a(n-1). - Emeric Deutsch (deutsch(AT)duke.poly.edu), Apr 01 2004
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PROGRAM
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(PARI) a(n)=if(n<0, 0, (7^n-(-1)^n)/8)
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CROSSREFS
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Adjacent sequences: A015549 A015550 A015551 this_sequence A015553 A015554 A015555
Sequence in context: A012872 A099322 A014989 this_sequence A091129 A091128 A025594
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KEYWORD
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nonn,easy
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AUTHOR
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Olivier Gerard (olivier.gerard(AT)gmail.com)
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