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A027063
a(n) = A027052(n, 2n-7).
2
0, 2, 6, 20, 68, 228, 754, 2456, 7884, 24982, 78282, 242998, 748364, 2289584, 6966346, 21098366, 63651808, 191406976, 573998990, 1717334182, 5127933348, 15286303526, 45503354154, 135287179508, 401809091392, 1192336418386
OFFSET
4,2
LINKS
MAPLE
T:= proc(n, k) option remember;
if k<0 or k>2*n then 0
elif k=0 or k=2 or k=2*n then 1
elif k=1 then 0
else add(T(n-1, k-j), j=1..3)
fi
end:
seq( T(n, 2*n-7), n=4..30); # G. C. Greubel, Nov 06 2019
MATHEMATICA
T[n_, k_]:= T[n, k]= If[k<0 || k>2*n, 0, If[k==0 || k==2 || k==2*n, 1, If[k==1, 0, Sum[T[n-1, k-j], {j, 3}]]]]; Table[T[n, 2*n-7], {n, 4, 30}] (* G. C. Greubel, Nov 06 2019 *)
PROG
(Sage)
@CachedFunction
def T(n, k):
if (k<0 or k>2*n): return 0
elif (k==0 or k==2 or k==2*n): return 1
elif (k==1): return 0
else: return sum(T(n-1, k-j) for j in (1..3))
[T(n, 2*n-7) for n in (4..30)] # G. C. Greubel, Nov 06 2019
CROSSREFS
Sequence in context: A148476 A148477 A369123 * A291005 A027065 A231057
KEYWORD
nonn
STATUS
approved