This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
| n | a(n) |
|---|---|
| 0 | 1 |
| 1 | 1 |
| 2 | 2 |
| 3 | 12 |
| 4 | 60 |
| 5 | 440 |
| 6 | 3810 |
| 7 | 37212 |
| 8 | 430696 |
| 9 | 5482080 |
| 10 | 78252390 |
| 11 | 1227201140 |
| 12 | 20955546348 |
| 13 | 388492703040 |
| 14 | 7745445183658 |
| 15 | 165550236166980 |
| 16 | 3773990094033360 |
| 17 | 91401848785134272 |
| 18 | 2344168680183033678 |
| 19 | 63455096201600595060 |
| 20 | 1808160553359068792020 |