OFFSET
0,2
LINKS
G. C. Greubel, Table of n, a(n) for n = 0..500
MATHEMATICA
T[n_, k_]:= T[n, k]= If[k==0, 1, If[k==n, 0, T[n-1, k] -3*T[n-1, k-1] +3*T[n, k-1] +T[n+1, k-1] ]];
Table[T[n, n-2], {n, 2, 30}] (* G. C. Greubel, Feb 18 2021 *)
PROG
(PARI) {a(n)=polcoeff((serreverse(x*(1-3*x+sqrt((1-3*x)*(1-7*x)+x*O(x^n)))/2/(1-3*x))/x)^2, n)}
(Sage)
@CachedFunction
def T(n, k):
if (k<0 or n<k): return 0
elif (k==0): return 1
elif (k==n): return 0
else: return T(n-1, k) - 3*T(n-1, k-1) + 3*T(n, k-1) + T(n+1, k-1)
[T(n, n-2) for n in (2..30)] # G. C. Greubel, Feb 18 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
Paul D. Hanna, Apr 26 2006
STATUS
approved