

A018933


From the game of Mousetrap.


1



2, 11, 50, 348, 2712, 23520, 225360, 2368800, 27135360, 336752640, 4503340800, 64585382400, 989138304000, 16115529830400, 278360283801600, 5081622594048000, 97772197146624000, 1977622100213760000
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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, 555560.


MAPLE

c := proc(n, x) local a, i; if n > x+1 then a := (n2)! ; for i from 3 to x do a := a+(1)^i*(binomial(x2, i2)+binomial(x3, i3))*(ni)! ; 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 = (n2)!; For[i = 3, i <= x, i++, a += (1)^i (Binomial[x2, i2] + Binomial[x3, i3]) (ni)!]]; a];
b[n_] := If[n == 5, 2, If[n == 6, 11, c[n, 5]]];
a[n_] := b[n + 5];
a /@ Range[0, 17] (* JeanFrançois 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



