OFFSET
0,1
LINKS
Daniel J. Mundfrom, A problem in permutations: the game of 'Mousetrap'. European J. Combin. 15 (1994), no. 6, 555-560.
MAPLE
c := proc(n, x) local a, i; if n > x+1 then a := (n-2)! ; for i from 3 to x do a := a+(-1)^i*(binomial(x-2, i-2)+binomial(x-3, i-3))*(n-i)! ; od: fi; a ; end: A018933 := proc(n) if n = 5 then 2 ; elif n = 6 then 11 ; else c(n, 5) ; fi: end: for n from 5 to 23 do printf("%d, ", A018933(n)) ; od: # R. J. Mathar, Oct 02 2008
MATHEMATICA
c[n_, x_] := Module[{a = 0, i}, If[n > x+1, a = (n-2)!; For[i = 3, i <= x, i++, a += (-1)^i (Binomial[x-2, i-2] + Binomial[x-3, i-3]) (n-i)!]]; a];
b[n_] := If[n == 5, 2, If[n == 6, 11, c[n, 5]]];
a[n_] := b[n + 5];
a /@ Range[0, 17] (* Jean-François Alcover, Apr 05 2020, after R. J. Mathar *)
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
This entry was corrupted by a misplaced edit Nov 30 2007; previous (and correct) version restored by N. J. A. Sloane Jan 25 2008
More terms from R. J. Mathar, Oct 02 2008
STATUS
approved