A211880 - OEIS

%I #19 Nov 26 2024 18:09:40

%S 0,0,0,2,0,20,40,210,1120,4760,25200,157850,800800,5345340,35035000,

%T 222472250,1648046400,12000388400,88529240800,720929459250,

%U 5786188408000,48072795270500,424300329453000,3731123025279650,34083741984292000,323768324084205000

%N Number of permutations of n elements with no fixed points and largest cycle of length 3.

%C a(n) = A055814(n) - A123023(n). - _Vaclav Kotesovec_, Oct 09 2013

%H Alois P. Heinz, <a href="/A211880/b211880.txt">Table of n, a(n) for n = 0..250</a>

%F E.g.f.: (exp(x^3/3)-1) * exp(x^2/2).

%F Recurrence: (n-3)*a(n) = (n-1)*(2*n-5)*a(n-2) + (n-3)*(n-2)*(n-1)*a(n-3) - (n-3)*(n-2)*(n-1)*a(n-4) - (n-4)*(n-3)*(n-2)*(n-1)*a(n-5). - _Vaclav Kotesovec_, Oct 09 2013

%e a(3) = 2: (2,3,1), (3,1,2).

%p egf:= (exp(x^3/3)-1)*exp(x^2/2):

%p a:= n-> n! *coeff(series(egf, x, n+1), x, n):

%p seq(a(n), n=0..30);

%t A[n_, k_] := A[n, k] = If[n < 0, 0, If[n == 0, 1,

%t      Sum[Product[n - i, {i, 1, j - 1}] A[n - j, k], {j, 2, k}]]];

%t T[n_, k_] := A[n, k] - If[k == 0, 0, A[n, k - 1]];

%t a[n_] := T[n, 3];

%t Table[a[n], {n, 0, 25}] (* _Jean-François Alcover_, Sep 03 2021, after _Alois P. Heinz_ in A211871 *)

%Y Column k=3 of A211871.

%Y Cf. A055814, A123023.

%K nonn

%O 0,4

%A _Alois P. Heinz_, Feb 13 2013