%I #5 Mar 30 2012 18:58:07
%S 0,0,1,5,20,180,5013,1016629,5282300384,5396635591915760,
%T 28512136651893281578375965,
%U 153869762066843605647265362776201153415021,4387155683474529138873327728747664927423052537019723373711103123120
%N a(n)=f(a(n-1)+1,a(n-2)+1,a(n-3)+1), where f(x,y,z)=yz+zx+xy and (a(1),a(2),a(3))=(0,0,1).
%C For a guide to related sequences, see A203761.
%t a[1] = 0; a[2] = 0; a[3] = 1;
%t a[n_] := SymmetricPolynomial[2, {1 + a[n - 1], 1 + a[n - 2], 1 + a[n - 3]}]
%t Table[a[n], {n, 1, 13}] (* A203902 *)
%Y Cf. A203761.
%K nonn
%O 1,4
%A _Clark Kimberling_, Jan 07 2012
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