OFFSET
0,4
REFERENCES
V. van der Noort and N. J. A. Sloane, Paper in preparation, 2007.
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..500
FORMULA
See A127080 for e.g.f.
MAPLE
Q:= proc(n, k) option remember;
if k<2 then 1
elif `mod`(k, 2)=0 then (n-k+1)*Q(n+1, k-1) - (k-1)*Q(n+2, k-2)
else ( (n-k+1)*Q(n+1, k-1) - (k-1)*(n+1)*Q(n+2, k-2) )/n
fi; end;
seq( Q(2, n), n=0..30); # G. C. Greubel, Jan 30 2020
MATHEMATICA
Q[n_, k_]:= Q[n, k]= If[k<2, 1, If[EvenQ[k], (n-k+1)*Q[n+1, k-1] - (k-1)*Q[n + 2, k-2], ((n-k+1)*Q[n+1, k-1] - (k-1)*(n+1)*Q[n+2, k-2])/n]]; Table[Q[2, k], {k, 0, 30}] (* G. C. Greubel, Jan 30 2020 *)
PROG
(Sage)
@CachedFunction
def Q(n, k):
if (k<2): return 1
elif (mod(k, 2)==0): return (n-k+1)*Q(n+1, k-1) - (k-1)*Q(n+2, k-2)
else: return ( (n-k+1)*Q(n+1, k-1) - (k-1)*(n+1)*Q(n+2, k-2) )/n
[Q(2, n) for n in (0..30)] # G. C. Greubel, Jan 30 2020
CROSSREFS
KEYWORD
sign
AUTHOR
N. J. A. Sloane, Mar 24 2007
STATUS
approved