# Recurrence relation

**Discrete Mathematics**Level pending

A barrel contains 2n balls , numbered 1 to 2n. Choose three balls at random , one after the other , and with the balls replaced after each draw. What is the probability that the three element sequence obtained has the properties that the smallest element is odd and that only the smallest element , if any , is repeated???

NOTE : refer to combinatorics of An EXCURSION IN MATHEMATICS