Can a Minecraft seed ever be recovered & Can you use the seeds from platform to platform?

I spent hours on a world and didn't know what seeds were so I just sold my xbox without writing down the seed or a picture… Is there any way I can get it back and use it cross plat?

I assume your talking about Xbox. I know on PC I use a program called Core to generate worlds and seeds you can try it and see if any of the seeds will work on your Xbox. http://rdevmobile.com/Core.exe