OFFSET
0,2
COMMENTS
If X is an n-set and Y_i (i=1,2,3,4) mutually disjoint 2-subsets of X then a(n-6) is equal to the number of 5-subsets of X intersecting each Y_i (i=1,2,3,4). - Milan Janjic, Aug 26 2007
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..1000
INRIA Algorithms Project, Encyclopedia of Combinatorial Structures 328
Milan Janjic, Two Enumerative Functions
Tanya Khovanova, Recursive Sequences
Luis Manuel Rivera, Integer sequences and k-commuting permutations, arXiv preprint arXiv:1406.3081 [math.CO], 2014-2015.
Leo Tavares, Illustration: Square Block Star Frames
Index entries for linear recurrences with constant coefficients, signature (2,-1).
FORMULA
a(n) = Sum_{k=1..8n} (i^k+1)*(i^(8n-k)+1), where i=sqrt(-1). - Bruno Berselli, Mar 19 2012
G.f.: 16*x/(x-1)^2. - Vincenzo Librandi, Jun 10 2013
MAPLE
MATHEMATICA
Range[0, 1000, 16] (* Vladimir Joseph Stephan Orlovsky, May 31 2011 *)
CoefficientList[Series[16 x / (x - 1)^2, {x, 0, 60}], x] (* Vincenzo Librandi Jun 10 2013 *)
PROG
(PARI) a(n)=16*n \\ Charles R Greathouse IV, Sep 24 2015
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved