It is hard to overestimate the importance of the OEIS in enumerative combinatorics.
I discovered the main results of my PhD thesis essentially as follows:
1. Find complicated construction A, hoping to prove some new results.
2. Fail to sufficiently understand/analyze A.
3. Write computer program to analyze characteristics of A for small n.
4. Using OEIS, discover that apparently A is (in some sense) equivalent to some completely different construction B, which is much simpler and well-understood.
5. Show desired result as well as further other results using B and variations of it.
I discovered the main results of my PhD thesis essentially as follows:
1. Find complicated construction A, hoping to prove some new results.
2. Fail to sufficiently understand/analyze A.
3. Write computer program to analyze characteristics of A for small n.
4. Using OEIS, discover that apparently A is (in some sense) equivalent to some completely different construction B, which is much simpler and well-understood.
5. Show desired result as well as further other results using B and variations of it.