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A027081
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a(n) = Sum_{k=0..2n-3} T(n,k) * T(n,k+3), with T given by A027052.
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2
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8, 56, 438, 3574, 29738, 249200, 2094902, 17648718, 148968822, 1259807224, 10674450652, 90618393250, 770728674864, 6567151658496, 56054864624310, 479267092351534, 4104271159315190, 35200977081482376, 302343415930398696, 2600408469332918538, 22394817457275426524
(list;
graph;
refs;
listen;
history;
text;
internal format)
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OFFSET
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3,1
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LINKS
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G. C. Greubel, Table of n, a(n) for n = 3..1000
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MAPLE
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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( add(T(n, k)*T(n, k+3), k=0..2*n-3), n=3..30); # G. C. Greubel, Nov 07 2019
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MATHEMATICA
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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[Sum[T[n, k]*T[n, k+3], {k, 0, 2*n-3}], {n, 3, 30}] (* G. C. Greubel, Nov 07 2019 *)
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PROG
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(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))
[sum(T(n, k)*T(n, k+3) for k in (0..2*n-3)) for n in (3..30)] # G. C. Greubel, Nov 07 2019
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CROSSREFS
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Sequence in context: A323699 A323700 A182430 * A093134 A001398 A251250
Adjacent sequences: A027078 A027079 A027080 * A027082 A027083 A027084
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KEYWORD
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nonn
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AUTHOR
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Clark Kimberling
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EXTENSIONS
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More terms from Sean A. Irvine, Oct 22 2019
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STATUS
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approved
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