I think he was already quite prolific before that started.

IMO, it is a bit of a myth that Adderall will make an already productive person more productive.

However, stimulants do motivate compulsive behaviors and rigid thinking.

That's where it would have helped Erdos. To just do math everyday and never be much interested in other pursuits takes something extra. Even into old age he didn't have anything else on the bucket list.