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A025231
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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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4
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2, 3, 12, 57, 300, 1686, 9912, 60213, 374988, 2381322, 15361896, 100389306, 663180024, 4421490924, 29712558576, 201046204173, 1368578002188, 9366084668802, 64403308499592, 444739795023054, 3082969991029800
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,1
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FORMULA
| G.f.: (1-sqrt(1-8*x+4*x^2))/2 - Michael Somos, Jun 08, 2000.
Another recurrence formula: n*a(n)=(8*n-12)*a(n-1)-(4*n-12)*a(n-2) [From Richard Choulet (richardchoulet(AT)yahoo.fr), Dec 16 2009]
G.f.: A(x)=(1-sqrt(1-8*x+4*x^2))/(2*x)= 1 + (1 - G(0))/x; G(k)= 1 + 2*x - 3*x/G(k+1); (continued fraction, 1-step ). - Sergei N. Gladkovskii, Jan 05 2012
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PROG
| (PARI) a(n)=polcoeff((1-sqrt(1-8*x+4*x^2+x*O(x^n)))/2, n)
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CROSSREFS
| Essentially the same as A047891.
Sequence in context: A002638 A027072 A083746 * A094532 A092980 A191464
Adjacent sequences: A025228 A025229 A025230 * A025232 A025233 A025234
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KEYWORD
| nonn,eigen
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AUTHOR
| Clark Kimberling (ck6(AT)evansville.edu)
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