1. The problem statement, all variables and given/known data Express (2n+1)(2n+3)(2n+5)...(4n-3)(4n-1) in terms of factorials 2. Relevant equations n!=n(n-1)! 3. The attempt at a solution I know (2n+1)+(2n+3)+⋯+(4n−1)=∑2n−1+2k, where k starts as k = 1 and increases to infinity. Then I was stuck. I am trying to learn maths on my own but it is getting more difficult.