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A026558
a(n) = T(2*n, n), where T is given by A026552.
18
1, 2, 7, 24, 93, 362, 1452, 5880, 24089, 99386, 412637, 1721500, 7211536, 30312960, 127790379, 540082784, 2287577537, 9707988994, 41269156159, 175705272784, 749099069183, 3197651758190, 13665035075871, 58456775063400, 250302852165368, 1072680809038112, 4600656305265352, 19746390910296372
OFFSET
0,2
LINKS
FORMULA
a(n) = A026552(2*n, n).
MATHEMATICA
T[n_, k_]:= T[n, k]= If[k==0 || k==2*n, 1, If[k==1 || k==2*n-1, Floor[(n+2)/2], If[EvenQ[n], T[n-1, k-2] + T[n-1, k] + T[n-1, k-1], T[n-1, k-2] + T[n-1, k]]]]; (* T=A026552 *)
a[n_]:= a[n]= Block[{$RecursionLimit = Infinity}, T[2*n, n]];
Table[a[n], {n, 0, 40}] (* G. C. Greubel, Dec 17 2021 *)
PROG
(Sage)
@CachedFunction
def T(n, k): # T = A026552
if (k==0 or k==2*n): return 1
elif (k==1 or k==2*n-1): return (n+2)//2
elif (n%2==0): return T(n-1, k) + T(n-1, k-1) + T(n-1, k-2)
else: return T(n-1, k) + T(n-1, k-2)
[T(2*n, n) for n in (0..40)] # G. C. Greubel, Dec 17 2021
KEYWORD
nonn
EXTENSIONS
Terms a(20) onward from G. C. Greubel, Dec 17 2021
STATUS
approved