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 A166748 E.g.f.: exp(6*arcsin(x)). 4
 1, 6, 36, 222, 1440, 9990, 74880, 609390, 5391360, 51798150, 539136000, 6060383550, 73322496000, 951480217350, 13198049280000, 195053444556750, 3061947432960000, 50908949029311750, 894088650424320000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS exp(6*arcsin(1/2)) is Aleksandr Gelfond's constant exp(Pi). LINKS G. C. Greubel, Table of n, a(n) for n = 0..445 A. R. Povolotsky et al., With regards to OEIS A166748, sci.math.symbolic usenet group, 2009 FORMULA Contribution from Alexander R. Povolotsky, Oct 24 2009: (Start) a(n+2) = (n^2+36)*a(n), a(0)=1, a(1)=6. The above recurrence leads to a(n) = (3*2^n*gamma(-3*i+n/2)*gamma(3*i+n/2)*(cos((n*Pi)/2)+i*sin((n*Pi)/2))*sinh(((6-i*n)*Pi)/2))/Pi where "i" is imaginary unit. (End) a(n) = 3*2^(n-1)*(exp(3*Pi)-(-1)^n*exp(-3*Pi))*|Gamma(n/2+3i)|^2/Pi. - R. J. Mathar and M. F. Hasler, Oct 25 2009 a(n) ~ 6 * (exp(3*Pi) - (-1)^n*exp(-3*Pi)) * n^(n-1) / exp(n). - Vaclav Kotesovec, Nov 06 2014 MATHEMATICA Round[Table[3*2^(n-1)*(E^(3*Pi)-(-1)^n*E^(-3*Pi))*Abs[Gamma[n/2+3*I]]^2/Pi, {n, 0, 20}]] (* Vaclav Kotesovec, Nov 06 2014 *) CoefficientList[Series[Exp[6*ArcSin[x]], {x, 0, 20}], x] * Range[0, 20]! (* Vaclav Kotesovec, Nov 06 2014 *) PROG (PARI) A166748(n)=round(norm(gamma(n/2+3*I))/Pi*if(n%2, cosh(3*Pi), sinh(3*Pi))*3<

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