OFFSET
0,3
COMMENTS
For n>=1, a(n) is equal to the number of functions f:{1,2,3,4,5,6}->{1,2,...,n} such that for a fixed x in {1,2,3,4,5,6} and a fixed y in {1,2,...,n} we have f(x)<>y. - Aleksandar M. Janjic and Milan Janjic, Mar 13 2007
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..1000
Milan Janjic, Enumerative Formulas for Some Functions on Finite Sets
Index entries for linear recurrences with constant coefficients, signature (7,-21,35,-35,21,-7,1).
FORMULA
G.f.: -2*x^2*(x^4+41*x^3+171*x^2+131*x+16)/(x-1)^7. - Colin Barker, Nov 06 2012
Sum_{n>=2} 1/a(n) = 5 - Sum_{k=2..5} zeta(k). - Amiram Eldar, Jul 05 2020
MATHEMATICA
f[n_]:=n^6-n^5; f[Range[0, 60]] (* Vladimir Joseph Stephan Orlovsky, Feb 10 2011 *)
Table[n^6 - n^5, {n, 0, 50}] (* Vincenzo Librandi, Aug 15 2016 *)
PROG
(PARI) a(n)=n^6-n^5 \\ Charles R Greathouse IV, Oct 07 2015
(Magma) [n^6-n^5: n in [0..40]]; // Vincenzo Librandi, Aug 15 2016
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
N. J. A. Sloane, Jul 05 2003
STATUS
approved