A018933 From the game of Mousetrap.

2, 11, 50, 348, 2712, 23520, 225360, 2368800, 27135360, 336752640, 4503340800, 64585382400, 989138304000, 16115529830400, 278360283801600, 5081622594048000, 97772197146624000, 1977622100213760000

Offset

0,1

Links

Table of n, a(n) for n=0..17.

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

Cf. A002468.

Sequence in context: A105486 A357548 A137960 * A116586 A119366 A034574

Adjacent sequences: A018930 A018931 A018932 * A018934 A018935 A018936

Keyword

nonn

Author

N. J. A. Sloane

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