This site is supported by donations to The OEIS Foundation.

 Hints (Greetings from The On-Line Encyclopedia of Integer Sequences!)
 A226730 a(n) = n! + (2*n-1)!/(n-1)!. 1
 2, 8, 66, 864, 15240, 333360, 8653680, 259499520, 8821975680, 335224915200, 14079333945600, 647648004326400, 32382382493260800, 1748648405555251200, 101421603773538048000, 6288139373806338048000, 415017197646001606656000, 29051203816724366204928000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS The product of the first parts of the partitions of 2n into exactly two parts plus the product of the second parts of the partitions of 2n into exactly two parts. LINKS Vincenzo Librandi, Table of n, a(n) for n = 1..370 FORMULA a(n) = n! + (2n-1)!/(n-1)!. E.g.f.: 1/(1 - x) + 1/(2*sqrt(1 - 4*x)) - 3/2. - Ilya Gutkovskiy, Dec 06 2016 EXAMPLE a(3) = 66, since 2(3) = 6 has 3 partitions with exactly two parts: (5,1), (4,2), and (3,3).  a(3) = 5*4*3 + 1*2*3 = 60 + 6 = 66. MATHEMATICA Table[n! + (2 n - 1)! / (n - 1)!, {n, 20}] (* Vincenzo Librandi, Feb 07 2018 *) PROG (MAGMA) [Factorial(n)+Factorial(2*n-1) div Factorial(n-1): n in [1..20]]; // Vincenzo Librandi, Feb 07 2018 CROSSREFS Sequence in context: A231280 A086594 A132219 * A202553 A023164 A053922 Adjacent sequences:  A226727 A226728 A226729 * A226731 A226732 A226733 KEYWORD nonn,easy AUTHOR Wesley Ivan Hurt, Jun 15 2013 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 October 16 15:51 EDT 2019. Contains 328101 sequences. (Running on oeis4.)