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 A025240 a(n) = a(1)*a(n-1) + a(2)*a(n-2) + ...+ a(n-2)*a(2) for n >= 3. 2
 3, 2, 6, 22, 90, 394, 1806, 8558, 41586, 206098, 1037718, 5293446, 27297738, 142078746, 745387038, 3937603038, 20927156706, 111818026018, 600318853926, 3236724317174, 17518619320890, 95149655201962, 518431875418926, 2832923350929742 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 LINKS FORMULA G.f.: (1+3*x-sqrt(1-6*x+x^2))/2 - Michael Somos, Jun 08, 2000. Conjecture: n*a(n) +3*(-2*n+3)*a(n-1) +(n-3)*a(n-2)=0. - R. J. Mathar, Feb 25 2015 MATHEMATICA Rest[CoefficientList[Series[(1+3x-Sqrt[1-6x+x^2])/2, {x, 0, 40}], x]] (* Harvey P. Dale, Aug 26 2013 *) PROG (PARI) a(n)=polcoeff((1+3*x-sqrt(1-6*x+x^2+x*O(x^n)))/2, n) CROSSREFS Essentially same as A006318. Sequence in context: A268642 A110768 A140230 * A137602 A086550 A266239 Adjacent sequences:  A025237 A025238 A025239 * A025241 A025242 A025243 KEYWORD nonn AUTHOR STATUS approved

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Last modified February 24 03:49 EST 2018. Contains 299595 sequences. (Running on oeis4.)