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%I
%S 0,1,2,3,4,7,10,13,16,21,26,31,36,43,50,57,64,73,82,91,100,111,122,
%T 133,144,157,170,183,196,211,226,241,256,273,290,307,324,343,362,381,
%U 400,421,442,463,484,507,530,553,576
%N Expansion of x(1+x^4)/((1-x)^2*(1-x^4)).
%C Number of 0..n-1 arrays of 5 elements with zero 2nd differences [From R. H. Hardin, Nov 15 2011]
%D Pach and Agarwal, Combinatorial Geometry, p. 220, Problem 13.10.
%F a(n) = 2*a(n-1) -a(n-2) +a(n-4) -2*a(n-5) +a(n-6) [From R. H. Hardin , Nov 15 2011]
%p f := n->n^2/4+3*n/2+g(n); g := n->if n mod 2 = 0 then 3 elif n mod 4 = 1 then 9/4 else 13/4; fi;
%o (PARI) Vec(x(1+x^4)/((1-x)^2*(1-x^4))+O(x^99)) \\ _Charles R Greathouse IV_, Sep 26 2012
%K nonn,easy
%O 0,3
%A _N. J. A. Sloane_.
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