What's the name of the story whose premise is that in the same way cheques never tear along the perforations, nothing is stronger than the material, the conclusion is, remove all the material and the remaining nothing, no longer weakened by material, will be the strongest and most immutable objects on Earth

The story you are referring to is called "The Nine Billion Names of God" by Arthur C. Clarke. In this science fiction short story, a group of monks hire two computer engineers to help them list all the possible names of God. Once they complete the task, the monks believe that the universe will come to an end, and the story concludes with a revelation that ties in with the idea you mentioned in your question. Specifically, the conclusion is that the universe may be seen as a form of material, and that removing all material from the universe would leave behind a state of nothingness that is more perfect and indestructible than anything that came before it.