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A026749
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a(n) = T(2n,n-1), T given by A026747.
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12
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1, 6, 30, 143, 671, 3132, 14601, 68101, 318035, 1487661, 6971222, 32727472, 153926409, 725264305, 3423262180, 16185240446, 76648901377, 363557014067, 1726994886004, 8215502584008, 39135887682617, 186676023857041, 891557875400175
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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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A026747 := proc(n, k) option remember;
if k=0 or k = n then 1;
elif type(n, 'even') and k <= n/2 then
procname(n-1, k-1)+procname(n-2, k-1)+procname(n-1, k) ;
else
procname(n-1, k-1)+procname(n-1, k) ;
end if ;
end proc:
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MATHEMATICA
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T[n_, k_]:= T[n, k]= If[k==0 || k==n, 1, If[EvenQ[n] && k<=n/2, T[n-1, k -1] + T[n-2, k-1] + T[n-1, k], T[n-1, k-1] + T[n-1, k] ]]; Table[T[2n, n-1], {n, 30}] (* G. C. Greubel, Oct 29 2019 *)
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PROG
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(Sage)
@CachedFunction
def T(n, k):
if (k==0 or k==n): return 1
elif (mod(n, 2)==0 and k<=n/2): return T(n-1, k-1) + T(n-2, k-1) + T(n-1, k)
else: return T(n-1, k-1) + T(n-1, k)
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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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