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 A026560 a(n) = T(2*n, n-2), where T is given by A026552. 18
 1, 4, 18, 74, 311, 1296, 5432, 22796, 95958, 404812, 1711600, 7250970, 30772989, 130810512, 556867224, 2373764416, 10130935783, 43285462884, 185129287262, 792525473552, 3395664830670, 14560682746632, 62482560679368, 268307898599664, 1152883194581155, 4956738399534376, 21323028570642414, 91775945084805898 (list; graph; refs; listen; history; text; internal format)
 OFFSET 2,2 LINKS G. C. Greubel, Table of n, a(n) for n = 2..1000 FORMULA a(n) = A026552(2*n, n-2). 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-2]]; Table[a[n], {n, 2, 40}] (* G. C. Greubel, Dec 18 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-2) for n in (2..40)] # G. C. Greubel, Dec 18 2021 CROSSREFS Cf. A026552, A026553, A026554, A026555, A026556, A026557, A026558, A026559, A026563, A026566, A026567, A027272, A027273, A027274, A027275, A027276. Sequence in context: A307323 A218059 A069008 * A180140 A245127 A037674 Adjacent sequences: A026557 A026558 A026559 * A026561 A026562 A026563 KEYWORD nonn AUTHOR Clark Kimberling EXTENSIONS Terms a(20) onward from G. C. Greubel, Dec 18 2021 STATUS approved

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Last modified September 15 10:23 EDT 2024. Contains 375932 sequences. (Running on oeis4.)