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) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 15 |
| 5 | 45 |
| 6 | 455 |
| 7 | 1330 |
| 8 | 20475 |
| 9 | 58905 |
| 10 | 1221759 |
| 11 | 3478761 |
| 12 | 90858768 |
| 13 | 256851595 |
| 14 | 8093990190 |
| 15 | 22760723700 |
| 16 | 840261910995 |
| 17 | 2353351951665 |
| 18 | 99615373765775 |
| 19 | 278110855548955 |
| 20 | 13278694407181203 |
| 21 | 36976937738226486 |