A122044 a(n) = a(n-2) - (n-3)*a(n-3), with a(0)=0, a(1)=1, a(2)=2.

0, 1, 2, 1, 1, -3, -2, -7, 13, 5, 62, -99, 17, -719, 1106, -923, 10453, -16407, 24298, -183655, 303217, -621019, 3792662, -6685359, 16834061, -90123923, 170597318, -494141387, 2423695393, -4929671655, 15765512842, -72793142659, 158725990837, -545758527919, 2415313413266

Offset

0,3

Links

G. C. Greubel, Table of n, a(n) for n = 0..1000

Formula

a(n) = a(n-2) - (n-3)*a(n-3), with a(0)=0, a(1)=1, a(2)=2. - G. C. Greubel, Oct 04 2019

Maple

a:= proc(n) option remember;
      if n < 3 then n
    else a(n-2)-(n-3)*a(n-3)
      fi;
    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]= a[n-2] - (n-3)*a[n-3]; Table[a[n], {n, 0, 35}]

Prog

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

Crossrefs

Cf. A122021, A122048, A122050.

Sequence in context: A156025 A035556 A296086 * A120744 A053423 A216201

Adjacent sequences: A122041 A122042 A122043 * A122045 A122046 A122047

Keyword

sign,easy

Author

Roger L. Bagula, Sep 13 2006

Extensions

Edited by N. J. A. Sloane, Sep 17 2006

More terms from Max Alekseyev, Sep 13 2009

Status

approved