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Search: id:A101502
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| A101502 |
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Number of closed walks on C_5 tensor J_2. |
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+0
2
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| 1, 0, 4, 0, 48, 32, 640, 896, 8960, 18432, 130048, 337920, 1941504, 5857280, 29605888, 98435072, 458424320, 1624375296, 7174881280, 26507476992, 113123524608, 429538672640, 1792440008704, 6929367695360, 28495396732928
(list; graph; listen)
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OFFSET
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0,3
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COMMENT
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Let (C_5 tensor J_2) be the 10 node graph whose adjacency matrix is the tensor product of that of C_5 and J_2=[1,1;1,1]. Then a(n) counts closed walks of length n at a vertex of the graph.
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REFERENCES
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E.R. van Dam, Graphs with few eigenvalues, Tilburg, 1968, p53.
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FORMULA
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G.f.: (1-2x-8x^2+8x^3)/((1-4x)(1+2x-4x^2)); a(n)=2a(n-1)+12a(n-2)-16a(n-3), n>4; a(n)=(sqrt(5)-1)^n/5+(-sqrt(5)-1)^n/5+4^n/10+0^n/2.
(1/10) [4^n - (-2)^(n+1)*Lucas(n) ], n>0. - Ralf Stephan, May 16 2007
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CROSSREFS
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Cf. A101501.
Sequence in context: A138546 A019217 A009371 this_sequence A118440 A013037 A129825
Adjacent sequences: A101499 A101500 A101501 this_sequence A101503 A101504 A101505
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KEYWORD
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easy,nonn
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AUTHOR
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Paul Barry (pbarry(AT)wit.ie), Dec 04 2004
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