OFFSET
1,2
COMMENTS
If Y and Z are 2-blocks of a (2n+1)-set X then a(n-2) is the number of 7-subsets of X intersecting both Y and Z. - Milan Janjic, Oct 28 2007
LINKS
Milan Janjic, Two Enumerative Functions
Index entries for linear recurrences with constant coefficients, signature (6,-15,20,-15,6,-1).
FORMULA
a(n) = n*(16*n^4 - 1)/15.
G.f.: x*(x^4+28*x^3+70*x^2+28*x+1) / (x-1)^6. - Colin Barker, Oct 06 2014
MATHEMATICA
LinearRecurrence[{6, -15, 20, -15, 6, -1}, {1, 34, 259, 1092, 3333, 8294}, 30] (* Harvey P. Dale, Feb 11 2024 *)
PROG
(PARI) Vec(x*(x^4+28*x^3+70*x^2+28*x+1)/(x-1)^6 + O(x^100)) \\ Colin Barker, Oct 06 2014
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Lekraj Beedassy, Apr 18 2003
EXTENSIONS
More terms from Ray Chandler, Oct 28 2003
STATUS
approved