A027031 a(n) = T(n,2n-7), T given by A027023.

1, 3, 9, 31, 105, 351, 1157, 3755, 12013, 37951, 118613, 367383, 1129345, 3449823, 10482869, 31713863, 95589753, 287224199, 860773781, 2573894583, 7681972113, 22890634939, 68116073369, 202458285647, 601159897137

Offset

4,2

Links

G. C. Greubel, Table of n, a(n) for n = 4..750

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-7), n=4..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-7], {n, 4, 30}] (* G. C. Greubel, Nov 05 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))
[T(n, 2*n-7) for n in (4..30)] # G. C. Greubel, Nov 05 2019

Crossrefs

Sequence in context: A148961 A148962 A148963 * A027094 A027033 A027096

Adjacent sequences: A027028 A027029 A027030 * A027032 A027033 A027034

Keyword

nonn

Author

Clark Kimberling

Status

approved