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Search: id:A007751
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| 0, 7, 120, 1921, 30624, 488071, 7778520, 123968257, 1975713600, 31487449351, 501823476024, 7997688167041, 127461187196640, 2031381306979207, 32374639724470680, 515962854284551681, 8223031028828356224
(list; graph; listen)
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OFFSET
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0,2
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REFERENCES
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Mentioned in a problem on p. 334 of Two-Year College Math. Jnl., Vol. 25, 1994.
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FORMULA
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G.f.: x(7+x)/((1-x)(1-16x+x^2)). a(n)=16a(n-1)-a(n-2)+8.
a(n)=-4/7+(2/7)*[8-3*sqrt(7)]^n+(2/7)*[8+3*sqrt(7)]^n+(1/14)*sqrt(7)*[8+3*sqrt(7)]^n-(1/14) *[8-3*sqrt(7)]^n*sqrt(7), with n>=0 - Paolo P. Lava (ppl(AT)spl.at), Jun 19 2008
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PROGRAM
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(PARI) a(n)=local(w); w=8+3*quadgen(28); imag(w^n)+4*(real(w^n)-1)/7
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CROSSREFS
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Cf. A007750, A007752.
Sequence in context: A057769 A113667 A092612 this_sequence A156955 A095752 A113267
Adjacent sequences: A007748 A007749 A007750 this_sequence A007752 A007753 A007754
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KEYWORD
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nonn
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AUTHOR
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John C. Hallyburton, Jr. [ hallyb(AT)vmsdev.enet.dec.com ].
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EXTENSIONS
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Edited by Michael Somos, Jul 27, 2002
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