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Search: id:A080097
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| 0, 3, 8, 24, 63, 168, 440, 1155, 3024, 7920, 20735, 54288, 142128, 372099, 974168, 2550408, 6677055, 17480760, 45765224, 119814915, 313679520, 821223648, 2149991423, 5628750624, 14736260448, 38580030723, 101003831720
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OFFSET
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0,2
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COMMENT
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a(n), a(n)+1 and a(n)+2 are consecutive members of A049997.
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FORMULA
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If n is odd, then a(n) = F(n+1)F(n+3) = F(n)F(n+4)-2, else a(n) = F(n)F(n+4) = F(n+1)F(n+3)-2, where F(n) = Fibonacci numbers (A000045).
(1/5) {Lucas(2n+4) - 2(-1)^n - 5}.
G.f.: (3x+2x^2-x^3)/(1-x^2)(1-2x-2x^2+x^3)).
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MATHEMATICA
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CoefficientList[Series[(3x+2x^2-x^3)/(1-x^2)(1-2x-2x^2+x^3)), {x, 0, 35}], x]
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CROSSREFS
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Equals A007598(n+2) - 1. Cf. A064831, A059840.
Sequence in context: A084920 A026556 A096001 this_sequence A096886 A056332 A091588
Adjacent sequences: A080094 A080095 A080096 this_sequence A080098 A080099 A080100
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KEYWORD
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easy,nonn
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AUTHOR
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Mario Catalani (mario.catalani(AT)unito.it), Jan 29 2003
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EXTENSIONS
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Edited by Ralf Stephan, May 15 2005
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