The link below is a live which takes you out of this site to a useful site of Port Forwarding Numbers.
"Service Name and Transport Protocol Port Number Registry" Designed for those who know what they are doing.
If you are unsure don't fiddle!
I have found this site useful as forwarding numbers have grown and grown.
The Idea that someone has taken the time to log and register the port numbers is fantastic.
You must have a basic knowledge of programming to start using the router and the numbers provided.
Now, heed the warning. If you change anything on your router ,your PC or your PI.
It is your own responsibility, thus not mine if your equipment goes belly up.
You are responsible.
This is a tool that will hopefully help you identify a port forward number on your router if you are unsure of its origins.
Here are two links just click on them.
1) >Protocol Port Number Registry
2) >Port Forwarding Ports List