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 A143522 a(n) = n-fold Dumont operator of x evaluated at x=1, y=1, z=2. 1
 1, 2, 5, 18, 93, 618, 4905, 45162, 474777, 5618322, 73895085, 1069104258, 16873062453, 288485314938, 5311769483025, 104789840677722, 2205098925335217, 49302142664941602, 1167150946521879765 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS The Dumont operator: D = y*z*dx + z*x*dy + x*y*dz is used to generate expansions for the Jacobi elliptic functions sn, cn and dn. LINKS FORMULA E.g.f.: 3/(3*cosh(sqrt(3)*x) - 2*sqrt(3)*sinh(sqrt(3)*x)). E.g.f.: 2*(3*cosh(sqrt(3)*x) + 2*sqrt(3)*sinh(sqrt(3)*x))/(7 - cosh(2*sqrt(3)*x)). G.f.: 1/Q(0), where Q(k) = 1 - 2*x*(2*k+1) - x^2*(k+1)^2/Q(k+1); (continued fraction). - Sergei N. Gladkovskii, Sep 27 2013 a(n) ~ n!*(2*sqrt(3)/log(7+4*sqrt(3)))^(n+1). - Vaclav Kotesovec, Oct 05 2013 EXAMPLE Given the Dumont operator: D = y*z*dx + z*x*dy + x*y*dz, illustrate a(n) = D^n x evaluated at x=1, y=1, z=2: D^0 x = x --> a(0) = 1; D^1 x = y*z --> a(1) = 2; D^2 x = (y^2 + z^2)*x --> a(2) = 5; D^3 x = 4*z*y*x^2 + (z*y^3 + z^3*y) --> a(3) = 18; D^4 x = (4*y^2 + 4*z^2)*x^3 + (y^4 + 14*z^2*y^2 + z^4)*x --> a(4) = 93; D^5 x = 16*z*y*x^4 + (44*z*y^3 + 44*z^3*y)*x^2 + (z*y^5 + 14*z^3*y^3 + z^5*y) --> a(5) = 618. MATHEMATICA CoefficientList[Series[3/(3*Cosh[Sqrt[3]*x] - 2*Sqrt[3]*Sinh[Sqrt[3]*x]), {x, 0, 20}], x]* Range[0, 20]! (* Vaclav Kotesovec, Oct 05 2013 *) PROG (PARI) {a(n)=local(F=x); if(n>=0, for(i=1, n, F=y*z*deriv(F, x)+z*x*deriv(F, y)+x*y*deriv(F, z))); subst(subst(subst(F, x, 1), y, 1), z, 2)} CROSSREFS Cf. A143523. Sequence in context: A057864 A320154 A032273 * A217389 A123310 A058119 Adjacent sequences: A143519 A143520 A143521 * A143523 A143524 A143525 KEYWORD nonn AUTHOR Paul D. Hanna, Aug 22 2008 STATUS approved

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Last modified December 3 19:41 EST 2022. Contains 358543 sequences. (Running on oeis4.)