The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A273983 a(n) = ((4*n)!! - (4*n-1)!!)/(4*n+1). 3
 1, 31, 2745, 487935, 145769625, 65830256415, 41892106080825, 35736278004165375, 39370290736153001625, 54420772423242699849375, 92234193751998833171261625, 188098544080793843475953349375, 454418941572893462364414856265625, 1283429428883663190972186961851609375 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS Sequence is inspired by A273889. The same argument in A273889 can be used here to prove the expression evaluates to integers. LINKS Chai Wah Wu, Table of n, a(n) for n = 1..202 PROG (Python) doublefac=lambda x:1 if x<2 else x*doublefac(x-2) for i in range(200):     print(i, (doublefac(4*i)-doublefac(4*i-1))//(4*i+1)) # Brian Cheung, Jun 15 2016 CROSSREFS Cf. A273889, A007912. Sequence in context: A302137 A136245 A262642 * A173563 A190527 A106205 Adjacent sequences:  A273980 A273981 A273982 * A273984 A273985 A273986 KEYWORD nonn AUTHOR Chai Wah Wu, Jun 05 2016 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 September 28 21:22 EDT 2021. Contains 347717 sequences. (Running on oeis4.)