What function is computed by the function Mystery(n) below? Express your answer as a summation and then give its closed form.

Mystery ( n ){ sum=0;

for ( i =1; i <= n ; i++)

for ( j =1; j <= i: j++)

sum++;

return ( sum ) ;

}

I got T(n)=3n^2+4n+3 but do not know how to express it in closed form. Can someone help me how to do it?