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A108261
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2nd order recursive series having the property that the product of any two adjacent terms is a triangular number, T(b) = b(b+1)/2 where b equals term a(n) of related series A108262.
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1
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2, 3, 12, 65, 374, 2175, 12672, 73853, 430442, 2508795, 14622324, 85225145, 496728542, 2895146103, 16874148072, 98349742325
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,1
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LINKS
| K. J. Ramsey, RecursiveSeriesProblem [Edited by Kenneth J. Ramsey, May 14 2011]
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FORMULA
| a(n) = 6*a(n-1) - a(n-2) - 4
a(n)=1+(1/8)*sqrt(2)*[3-2*sqrt(2)]^n+(1/2)*[3+2*sqrt(2)]^n-(1/8)*[3+2*sqrt(2)]^n*sqrt(2)+(1/2)*[3-2*sqrt(2)]^n, with n>=0 - Paolo P. Lava (paoloplava(AT)gmail.com), Jun 25 2008
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EXAMPLE
| a(7)=12672
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CROSSREFS
| Cf. A108262.
Sequence in context: A188588 A032133 A155579 * A013152 A012911 A099805
Adjacent sequences: A108258 A108259 A108260 * A108262 A108263 A108264
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KEYWORD
| nonn
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AUTHOR
| Kenneth John Ramsey (RamseyKK2(AT)aol.com), May 29 2005
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