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A025239
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a(n) = a(1)*a(n-1) + a(2)*a(n-2) + ...+ a(n-2)*a(2) for n >= 3.
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0
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2, 3, 6, 21, 78, 318, 1356, 5997, 27222, 126138, 594132, 2836290, 13692300, 66729180, 327855768, 1622216829, 8076311142, 40427919714, 203353800324, 1027318915254, 5210182030308, 26517609163812, 135397544040744, 693364054299474
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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FORMULA
| G.f.: (1-sqrt(1-4*x-8*x^2))/2 - Michael Somos, Jun 08, 2000.
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MATHEMATICA
| Join[{2}, Drop[CoefficientList[Series[(1-Sqrt[1-4x-8x^2])/2, {x, 0, 30}], x], 2]] (* From Harvey P. Dale, Nov 05 2011 *)
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PROG
| (PARI) a(n)=polcoeff((1-sqrt(1-4*x-8*x^2+x*O(x^n)))/2, n)
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CROSSREFS
| Essentially the same as A025229.
Sequence in context: A000372 A123930 A125601 * A127294 A012924 A024485
Adjacent sequences: A025236 A025237 A025238 * A025240 A025241 A025242
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KEYWORD
| nonn
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AUTHOR
| Clark Kimberling (ck6(AT)evansville.edu)
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