All odd numbers can be represented by 2n+1 where n≥0 is an integer.
One part is 20/5=4 units. Now add the odd number to 4: 4+2n+1=2n+5, assuming that the odd number is added to each of the 5 parts.
The new part is 2n+5, so 5 of them make 5(2n+5)=10n+25. This is the quantity that 20 becomes. When n=0, 20 becomes 25 and when n=1, 20 becomes 35, and so on.