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 A027081 a(n) = Sum_{k=0..2n-3} T(n,k) * T(n,k+3), with T given by A027052. 2
 8, 56, 438, 3574, 29738, 249200, 2094902, 17648718, 148968822, 1259807224, 10674450652, 90618393250, 770728674864, 6567151658496, 56054864624310, 479267092351534, 4104271159315190, 35200977081482376, 302343415930398696, 2600408469332918538, 22394817457275426524 (list; graph; refs; listen; history; text; internal format)
 OFFSET 3,1 LINKS G. C. Greubel, Table of n, a(n) for n = 3..1000 MAPLE 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+3), k=0..2*n-3), n=3..30); # G. C. Greubel, Nov 07 2019 MATHEMATICA 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+3], {k, 0, 2*n-3}], {n, 3, 30}] (* G. C. Greubel, Nov 07 2019 *) PROG (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+3) for k in (0..2*n-3)) for n in (3..30)] # G. C. Greubel, Nov 07 2019 CROSSREFS Sequence in context: A323699 A323700 A182430 * A093134 A001398 A251250 Adjacent sequences: A027078 A027079 A027080 * A027082 A027083 A027084 KEYWORD nonn AUTHOR EXTENSIONS More terms from Sean A. Irvine, Oct 22 2019 STATUS approved

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Last modified March 23 04:41 EDT 2023. Contains 361434 sequences. (Running on oeis4.)