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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 (list; graph; refs; listen; history; text; internal format)
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
CROSSREFS
Sequence in context: A150400 A150401 A003041 * A150402 A151295 A150403
KEYWORD
nonn
AUTHOR
EXTENSIONS
Terms a(20) onward from G. C. Greubel, Dec 17 2021
STATUS
approved

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Last modified March 29 04:23 EDT 2024. Contains 371264 sequences. (Running on oeis4.)