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A025228
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a(n) = a(1)*a(n-1) + a(2)*a(n-2) + ...+ a(n-1)*a(1) for n >= 3.
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5
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2, 1, 4, 17, 76, 354, 1704, 8421, 42508, 218318, 1137400, 5996938, 31940792, 171605956, 928931280, 5061593709, 27739833228, 152809506582, 845646470616, 4699126915422, 26209721959656, 146681521121244, 823429928805936, 4635568494271458
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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COMMENTS
| Essentially A005572 shifted right twice, and 2 prepended.
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FORMULA
| G.f.: (1-sqrt(1-8*x+12*x^2))/2 - Michael Somos, Jun 08, 2000.
Another recurrence formula: n*a(n)=(8*n-12)*a(n-1)-12*(n-3)*a(n-2). [From Richard Choulet (richardchoulet(AT)yahoo.fr), Dec 16 2009]
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MATHEMATICA
| Rest[CoefficientList[Series[(1-Sqrt[1-8x+12x^2])/2, {x, 0, 30}], x]] (* From Harvey P. Dale, Apr 20 2011 *)
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PROG
| (PARI) a(n)=polcoeff((1-sqrt(1-8*x+12*x^2+x*O(x^n)))/2, n)
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CROSSREFS
| Sequence in context: A162977 A032174 A087801 * A132945 A192494 A013156
Adjacent sequences: A025225 A025226 A025227 * A025229 A025230 A025231
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KEYWORD
| nonn
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AUTHOR
| Clark Kimberling (ck6(AT)evansville.edu)
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