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Search: id:A128535
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| A128535 |
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F(n)*L(n-2) where F=Fibonacci and L=Lucas numbers. |
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+0
4
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| 0, -1, 2, 2, 9, 20, 56, 143, 378, 986, 2585, 6764, 17712, 46367, 121394, 317810, 832041, 2178308, 5702888, 14930351, 39088170
(list; graph; listen)
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OFFSET
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0,3
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COMMENT
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Generally, F(n)*L(n+k) = F(2*n + k) + F(k)*(-1)^(n+1). If k=0 the sequence is A001906; if k=1 it is A081714.
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FORMULA
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a(n) = F(2*(n-1)) - (-1)^(n+1), assuming F(0)=0 and L(0)=2.
a(n)=2*a(n-1)+2*a(n-2)-a(n-3). G.f.: x*(-1+4*x)/((1+x)*(x^2-3*x+1)). [From R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Apr 16 2009]
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EXAMPLE
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a(7) = 143 because F(7)*L(5) = 13*11.
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CROSSREFS
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Cf. A001906, A081714, A128533, A128534.
Sequence in context: A039796 A007024 A019223 this_sequence A081086 A019514 A135816
Adjacent sequences: A128532 A128533 A128534 this_sequence A128536 A128537 A128538
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KEYWORD
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easy,sign
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AUTHOR
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Axel Harvey (ax(AT)hirsig.ca), Mar 09 2007
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