This site is supported by donations to The OEIS Foundation.

 Please make a donation to keep the OEIS running. We are now in our 55th year. In the past year we added 12000 new sequences and reached 8000 citations (which often say "discovered thanks to the OEIS"). We need to raise money to hire someone to manage submissions, which would reduce the load on our editors and speed up editing. Other ways to donate

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A126965 a(n) = (2*n)!*(2*n-1)/(2^n*n!). 2
 -1, 1, 9, 75, 735, 8505, 114345, 1756755, 30405375, 585810225, 12439852425, 288735522075, 7273385294175, 197646339515625, 5763367260275625, 179518217255251875, 5948862302837829375, 208977775735174070625, 7757508341684492015625, 303429397707601987696875 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,3 REFERENCES V. van der Noort and N. J. A. Sloane, Paper in preparation, 2007. LINKS G. C. Greubel, Table of n, a(n) for n = 0..250 FORMULA E.g.f.: (1-4*x)^(1/2)/(1-2*x). G.f.: x - 1 + 9*x^2/(Q(0)-9*x), where Q(k)= 1 + 9*x + 2*k*(1+6*x) + 4*x*k^2 - x*(2*k+1)*(2*k+5)^2/Q(k+1); (continued fraction). - Sergei N. Gladkovskii, Apr 25 2013 a(n) = 1/sqrt(Pi) * Numerator(Gamma((2n+3)/2) - Gamma((2n+1)/2)), for n>=0. Denominators are 2^(n+1). - Richard R. Forberg, Feb 22 2015 +(-2*n+3)*a(n) +(2*n-1)^2*a(n-1)=0. - R. J. Mathar, Jun 17 2016 MATHEMATICA Table[((2n)!(2n-1))/(2^n n!), {n, 0, 20}] (* Harvey P. Dale, Jan 16 2017 *) PROG (PARI) for(n=0, 25, print1(((2*n)!*(2*n-1))/(2^n* n!), ", ")) \\ G. C. Greubel, Mar 19 2017 CROSSREFS Cf. A001147. Sequence in context: A223204 A136659 A231592 * A066222 A080254 A190916 Adjacent sequences:  A126962 A126963 A126964 * A126966 A126967 A126968 KEYWORD sign AUTHOR N. J. A. Sloane, Mar 21 2007 STATUS approved

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

Last modified December 15 15:10 EST 2019. Contains 329999 sequences. (Running on oeis4.)