A027030 a(n) = T(n,2n-6), T given by A027023.

1, 1, 5, 17, 57, 189, 613, 1949, 6097, 18825, 57525, 174353, 525049, 1573077, 4693909, 13960805, 41415089, 122603341, 362343053, 1069436317, 3152995209, 9287942097, 27341397469, 80443393889, 236581555233, 695561538977

Offset: 3

Author

Clark Kimberling

Keywords

• nonn

Links

• G. C. Greubel, Table of n, a(n) for n = 3..750

Programs

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(T(n,2*n-6), n=3..30); # G. C. Greubel, Nov 05 2019

Mathematica

T[n_, k_]:= T[n, k]= If[n<0, 0, If[k<3 || k==2*n, 1, Sum[T[n-1, k-j], {j, 3}]]]; Table[T[n, 2*n-6], {n,3,30}] (* G. C. Greubel, Nov 05 2019 *)

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))
[T(n, 2*n-6) for n in (3..30)] # G. C. Greubel, Nov 04 2019