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A143079
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a(n) = ((9+sqrt(9))^n + (9-sqrt(9))^n)/2.
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8
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1, 9, 90, 972, 11016, 128304, 1516320, 18055872, 215830656, 2584929024, 30988915200, 371685583872, 4459138615296, 53503133036544, 641998414356480, 7703745879785472, 92443540002471936, 1109314016699940864
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OFFSET
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0,2
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COMMENTS
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LINKS
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FORMULA
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a(n) = 18*a(n-1) - 72*a(n-2).
a(n) = 6^n*(2^n+1)/2.
G.f.: (1-9x)/(1-18x+72x^2). (End)
a(n) = (12^n + 6^n)/2.
G.f.: (1-9x)/((1-12x)(1-6x)). (End)
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PROG
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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Al Hakanson (hawkuu(AT)gmail.com), Oct 15 2008
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EXTENSIONS
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STATUS
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approved
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