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A027047
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a(n) = Sum_{k=0..2n-1} T(n,k) * T(n,k+1), with T given by A027023.
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2
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2, 8, 50, 336, 2418, 18088, 138850, 1086016, 8617122, 69159896, 560290322, 4574820624, 37603654098, 310873702392, 2582964183874, 21556333188288, 180609299685954, 1518572497996568, 12808849866774002, 108351496132761104, 918964407713589618, 7812768025080427672
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OFFSET
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1,1
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LINKS
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MAPLE
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T:= proc(n, k) option remember;
if k<3 or k=2*n then 1
else add(T(n-1, k-j), j=1..3)
fi
end:
seq(add(T(n, k)*T(n, k+1), k=0..2*n-1), n=1..30); # G. C. Greubel, Nov 04 2019
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MATHEMATICA
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T[n_, k_]:= T[n, k]= If[k<3 || k==2*n, 1, Sum[T[n-1, k-j], {j, 3}]]; Table[Sum[T[n, k]*T[n, k+1], {k, 0, 2*n-1}], {n, 1, 30}] (* G. C. Greubel, Nov 04 2019 *)
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PROG
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(Sage)
@CachedFunction
def T(n, k):
if (k<3 or k==2*n): return 1
else: return sum(T(n-1, k-j) for j in (1..3))
[sum(T(n, k)*T(n, k+1) for k in (0..2*n-1)) for n in (1..30)] # G. C. Greubel, Nov 04 2019
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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