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A027029 a(n) = T(n,2n-5), T given by A027023.

%I A027029 #8 Nov 05 2019 01:00:30
%S A027029 1,3,9,31,101,319,985,2991,8973,26687,78877,232083,680645,1991487,
%T A027029 5817073,16971415,49474389,144149959,419869065,1222785111,3561052305,
%U A027029 10371483259,30211361481,88022087975,256521698097,747794233779
%N A027029 a(n) = T(n,2n-5), T given by A027023.
%H A027029 G. C. Greubel, <a href="/A027029/b027029.txt">Table of n, a(n) for n = 3..750</a>
%p A027029 T:= proc(n, k) option remember;
%p A027029       if k<3 or k=2*n then 1
%p A027029     else add(T(n-1, k-j), j=1..3)
%p A027029       fi
%p A027029     end:
%p A027029 seq(T(n, 2*n-5), n=3..30); # _G. C. Greubel_, Nov 04 2019
%t A027029 T[n_, k_]:= T[n, k]= If[k<3 || k==2*n, 1, Sum[T[n-1, k-j], {j, 3}]]; Table[T[n, 2*n-5], {n, 3, 30}] (* _G. C. Greubel_, Nov 04 2019 *)
%o A027029 (Sage)
%o A027029 @CachedFunction
%o A027029 def T(n, k):
%o A027029     if (k<3 or k==2*n): return 1
%o A027029     else: return sum(T(n-1, k-j) for j in (1..3))
%o A027029 [T(n, 2*n-5) for n in (3..30)] # _G. C. Greubel_, Nov 04 2019
%K A027029 nonn
%O A027029 3,2
%A A027029 _Clark Kimberling_