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%I #8 Jul 03 2024 09:28:21
%S 3,4,18,5,23,6,189,102,420,291,41,7,711,48,1551,605,8,281,4433,2574,
%T 72,9,7007,1456,81,10,39039,27924,15834,7014,2370,588,82654,66963,
%U 43758,22848,9384,2958,111,11,149617,110721,66606,32232,12342,122,314925
%N a(n) = A028321(n)/2.
%H G. C. Greubel, <a href="/A051473/b051473.txt">Table of n, a(n) for n = 0..1000</a>
%t b:= Table[If[n<2, 1, Binomial[n,k] +3*Binomial[n-2,k-1]], {n,0,30}, {k, Floor[n/2]+1,n}]//Flatten;
%t Select[b, EvenQ]/2 (* _G. C. Greubel_, Jul 02 2024 *)
%o (Magma)
%o T:= func< n, k | n le 1 select 1 else Binomial(n, k) + 3*Binomial(n-2, k-1) >; // T = A028323
%o b:=[T(n, k): k in [1+Floor(n/2)..n], n in [0..100]];
%o [b[n]/2: n in [1..150] | (b[n] mod 2) eq 0]; // _G. C. Greubel_, Jul 02 2024
%o (SageMath)
%o def A028323(n, k): return binomial(n, k) + 3*binomial(n-2, k-1) - 3*int(n==0)
%o b=flatten([[A028323(n, k) for k in range(1+(n//2),n+1)] for n in range(101)])
%o [b[n]/2 for n in (1..150) if b[n]%2==0] # _G. C. Greubel_, Jul 02 2024
%Y Cf. A028313, A028314, A028315, A028316, A028317, A028318, A028319.
%Y Cf. A028320, A028321, A028322, A028323, A028324, A028325, A051472.
%K nonn
%O 0,1
%A _James A. Sellers_
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