Análisis: Sn=vector a1(vector a2+vector a3+...+vector an)
=vector a1(vector a1+vector d+vector a1+2 vector d+.. .+vector a1+(n-1)vector d)
=vector a1[(n-1)vector a1+n(n-1)vector d/2]
= 4(n-1)-1/2 n(n-1)/2
=-n^2/4+17n/4-4
Cuando n=17, toma el valor máximo.