A027049 a(n) = Sum_{k=0..2n-3} T(n,k) * T(n,k+3), with T given by A027023.

16, 120, 952, 7848, 65580, 550476, 4631876, 39047764, 329784608, 2790469092, 23656401612, 200928615160, 1709781846028, 14575407966156, 124466311279620, 1064636218853556, 9120848372291680, 78256468639080460, 672393605270681188, 5785139333187494936, 49838058776228021388

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<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+3), k=0..2*n-3), n=3..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+3], {k, 0, 2*n-3}], {n, 3, 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+3) for k in (0..2*n-3)) for n in (3..30)] # G. C. Greubel, Nov 04 2019

Crossrefs

Sequence in context: A324066 A164542 A351383 * A060219 A185760 A301649

Adjacent sequences: A027046 A027047 A027048 * A027050 A027051 A027052

Keyword

nonn

Author

Clark Kimberling

Extensions

More terms from Sean A. Irvine, Oct 22 2019

Status

approved