The following Summation

Question

1 2 1 2 1 2
------ x - + ------ x - + ------ x -
1+(2/n) n 1+(4/n) n 1+(6/n) n

is a right Riemann sum for this integral
�ç f(x)dx With subintervals [1,3]

can someone help me solve for the inegrand which is f(x).?