A027064 - OEIS

%I #11 Nov 07 2019 08:28:23

%S 1,1,3,11,37,125,421,1405,4637,15125,48777,155665,492157,1543269,

%T 4804663,14865495,45745953,140118817,427445507,1299383403,3937901525,

%U 11902380845,35891429675,108009437323,324455779889,973119941425

%N a(n) = A027052(n, 2n-8).

%H G. C. Greubel, <a href="/A027064/b027064.txt">Table of n, a(n) for n = 4..750</a>

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

%p       if k<0 or k>2*n then 0

%p     elif k=0 or k=2 or k=2*n then 1

%p     elif k=1 then 0

%p     else add(T(n-1, k-j), j=1..3)

%p       fi

%p     end:

%p seq( T(n,2*n-8), n=4..30); # _G. C. Greubel_, Nov 06 2019

%t 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-8], {n,4,30}] (* _G. C. Greubel_, Nov 06 2019 *)

%o (Sage)

%o @CachedFunction

%o def T(n, k):

%o     if (k<0 or k>2*n): return 0

%o     elif (k==0 or k==2 or k==2*n): return 1

%o     elif (k==1): return 0

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

%o [T(n,2*n-8) for n in (4..30)] # _G. C. Greubel_, Nov 06 2019

%K nonn

%O 4,3

%A _Clark Kimberling_