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A122653
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a(n) = 10*a(n-1) - a(n-2) with a(0)=0, a(1)=6.
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3
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0, 6, 60, 594, 5880, 58206, 576180, 5703594, 56459760, 558894006, 5532480300, 54765908994, 542126609640, 5366500187406, 53122875264420, 525862252456794, 5205499649303520, 51529134240578406, 510085842756480540, 5049329293324226994, 49983207090485789400
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OFFSET
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0,2
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COMMENTS
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Kekulé numbers for the benzenoids P''(n).
Numbers n such that 6*n^2 + 9 is a square. - Colin Barker, Mar 17 2014
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REFERENCES
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S. J. Cyvin and I. Gutman, Kekulé structures in benzenoid hydrocarbons, Lecture Notes in Chemistry, No. 46, Springer, New York, 1988 (p. 301).
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LINKS
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FORMULA
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MATHEMATICA
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LinearRecurrence[{10, -1}, {0, 6}, 30] (* Harvey P. Dale, Dec 16 2014 *)
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PROG
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(PARI) a(n)=if(n<2, (n%2)*6, 10*a(n-1)-a(n-2)) \\ Benoit Cloitre, Sep 23 2006
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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