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sum(N,X,S) :- N >= 2, sum(N,X,0,S) . sum(I,X,T,S) :- I >= 2, f(I,X,V), T1 is T+V, I1 is I-1, sum(I1,X,T1,S) . sum(1,_,S,S) . f(I,X,V) :- V is (4 * X + I)**2 / (2*I) .