For any integer n  1, then  k = 1 n k ( k + 2 )   is equal to?

Dear student
k=1nk(k+2)=k=1nk2+2k=k=1nk2+2k=1nk=n(n+1)(2n+1)6+2n(+1)2=n(n+1)(2n+1)6+n(n+1)=n(n+1)(2n+1)+6n(n+1)6=n(n+1)2n+1+66=n(n+1)(2n+7)7
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