OFFSET
0,3
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..1000
FORMULA
a(n) = a(n-1) - (n-4)*a(n-4).
MAPLE
a:= proc (n) option remember;
if n < 3 then n
elif n = 3 then 1
else a(n-1) - (n-4)*a(n-4)
end if
end proc:
seq(a(n), n = 0..30); # G. C. Greubel, Oct 04 2019
MATHEMATICA
a[0]=0; a[1]=1; a[2]=2; a[3]=1; a[n_]:= a[n]= a[n-1] - (n-4)*a[n-4]; Table[a[n], {n, 0, 40}]
PROG
(PARI) my(m=40, v=concat([0, 1, 2, 1], vector(m-4))); for(n=5, m, v[n] = v[n-1] - (n-5)*v[n-4] ); v \\ G. C. Greubel, Oct 04 2019
(Magma) I:=[0, 1, 2, 1]; [n le 4 select I[n] else Self(n-1) - (n-5)*Self(n-4): n in [1..40]]; // G. C. Greubel, Oct 04 2019
(Sage)
def a(n):
if n<3: return n
elif n==3: return 1
else: return a(n-1) - (n-4)*a(n-4)
[a(n) for n in (0..40)] # G. C. Greubel, Oct 04 2019
(GAP) a:=[0, 1, 2, 1];; for n in [5..30] do a[n]:=a[n-1]-(n-5)*a[n-4]; od; a; # G. C. Greubel, Oct 04 2019
CROSSREFS
KEYWORD
sign
AUTHOR
Roger L. Bagula, Sep 13 2006
EXTENSIONS
Terms a(31) onward added by G. C. Greubel, Oct 04 2019
STATUS
approved