A122048 a(n) = (n-2)*a(n-2) - a(n-3), with a(0)=0, a(1)=1, a(2)=2.

0, 1, 2, 1, 3, 1, 11, 2, 65, 3, 518, -38, 5177, -936, 62162, -17345, 871204, -322337, 13956609, -6350933, 251541299, -134624336, 5037176913, -3078652355, 110952516422, -75846181078, 2665939046483, -2007107043372, 69390261389636, -56857829217527, 1944934425953180

Offset

0,3

Links

G. C. Greubel, Table of n, a(n) for n = 0..800

Formula

a(n) = (n-2)*a(n-2) - a(n-3).

Maple

a:= proc (n) option remember;
      if n < 3 then n
    elif n = 3 then 1
    else (n-2)*a(n-2) - a(n-3)
      end if
    end proc:
seq(a(n), n = 0..35); # G. C. Greubel, Oct 04 2019

Mathematica

a[0]=0; a[1]=1; a[2]=2; a[n_]:= a[n]= (n-2)*a[n-2] - a[n-3]; Table[a[n], {n, 0, 35}]

Prog

(PARI) my(m=35, v=concat([0, 1, 2, 1], vector(m-4))); for(n=5, m, v[n] = (n-3)*v[n-2] - v[n-3] ); v \\ G. C. Greubel, Oct 04 2019
(Magma) I:=[0, 1, 2, 1]; [n le 4 select I[n] else (n-3)*Self(n-2) - Self(n-3): n in [1..35]]; // G. C. Greubel, Oct 04 2019
(Sage)
def a(n):
    if n<3: return n
    elif n==3: return 1
    else: return (n-2)*a(n-2) - a(n-3)
[a(n) for n in (0..35)] # G. C. Greubel, Oct 04 2019
(GAP) a:=[0, 1, 2, 1];; for n in [5..35] do a[n]:=(n-3)*a[n-2]-a[n-3]; od; a; # G. C. Greubel, Oct 04 2019

Crossrefs

Cf. A122021.

Sequence in context: A237978 A337276 A098570 * A046208 A195909 A195697

Adjacent sequences: A122045 A122046 A122047 * A122049 A122050 A122051

Keyword

sign

Author

Roger L. Bagula, Sep 13 2006

Extensions

Offset changed by G. C. Greubel, Oct 04 2019

Status

approved