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A027079
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a(n) = Sum_{k=0..2n-1} T(n,k) * T(n,k+1), with T given by A027052.
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2
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0, 4, 24, 160, 1136, 8420, 64224, 499984, 3952928, 31634724, 255682432, 2083562368, 17097573344, 141143273396, 1171240794072, 9763809318912, 81724975129664, 686539343850164
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OFFSET
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1,2
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LINKS
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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+1), k=0..2*n-1), n=1..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+1], {k, 0, 2*n-1}], {n, 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+1) for k in (0..2*n-1)) for n in (1..30)] # G. C. Greubel, Nov 07 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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STATUS
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approved
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