A027063 a(n) = A027052(n, 2n-7).

0, 2, 6, 20, 68, 228, 754, 2456, 7884, 24982, 78282, 242998, 748364, 2289584, 6966346, 21098366, 63651808, 191406976, 573998990, 1717334182, 5127933348, 15286303526, 45503354154, 135287179508, 401809091392, 1192336418386

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<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( T(n, 2*n-7), n=4..30); # G. C. Greubel, Nov 06 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[T[n, 2*n-7], {n, 4, 30}] (* G. C. Greubel, Nov 06 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))
[T(n, 2*n-7) for n in (4..30)] # G. C. Greubel, Nov 06 2019

Crossrefs

Sequence in context: A148476 A148477 A369123 * A291005 A027065 A231057

Adjacent sequences: A027060 A027061 A027062 * A027064 A027065 A027066

Keyword

nonn

Author

Clark Kimberling

Status

approved