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A027047 a(n) = Sum_{k=0..2n-1} T(n,k) * T(n,k+1), with T given by A027023. 2
2, 8, 50, 336, 2418, 18088, 138850, 1086016, 8617122, 69159896, 560290322, 4574820624, 37603654098, 310873702392, 2582964183874, 21556333188288, 180609299685954, 1518572497996568, 12808849866774002, 108351496132761104, 918964407713589618, 7812768025080427672 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

G. C. Greubel, Table of n, a(n) for n = 1..1000

MAPLE

T:= proc(n, k) option remember;

      if k<3 or k=2*n then 1

    else add(T(n-1, k-j), j=1..3)

      fi

    end:

seq(add(T(n, k)*T(n, k+1), k=0..2*n-1), n=1..30); # G. C. Greubel, Nov 04 2019

MATHEMATICA

T[n_, k_]:= T[n, k]= If[k<3 || k==2*n, 1, Sum[T[n-1, k-j], {j, 3}]]; Table[Sum[T[n, k]*T[n, k+1], {k, 0, 2*n-1}], {n, 1, 30}] (* G. C. Greubel, Nov 04 2019 *)

PROG

(Sage)

@CachedFunction

def T(n, k):

    if (k<3 or k==2*n): return 1

    else: return sum(T(n-1, k-j) for j in (1..3))

[sum(T(n, k)*T(n, k+1) for k in (0..2*n-1)) for n in (1..30)] # G. C. Greubel, Nov 04 2019

CROSSREFS

Sequence in context: A046165 A227264 A114619 * A034491 A231352 A186182

Adjacent sequences:  A027044 A027045 A027046 * A027048 A027049 A027050

KEYWORD

nonn

AUTHOR

Clark Kimberling

EXTENSIONS

More terms from Sean A. Irvine, Oct 22 2019

STATUS

approved

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Last modified September 30 08:55 EDT 2022. Contains 357104 sequences. (Running on oeis4.)