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) |
|---|---|
| 2 | 1 |
| 3 | 5 |
| 4 | 20 |
| 5 | 124 |
| 6 | 744 |
| 7 | 5928 |
| 8 | 47424 |
| 9 | 426816 |
| 10 | 4268160 |
| 11 | 50578560 |
| 12 | 606942720 |
| 13 | 8369256960 |
| 14 | 117169597440 |
| 15 | 1757543961600 |
| 16 | 28120703385600 |
| 17 | 498974747443200 |
| 18 | 8981545453977600 |
| 19 | 177051737331302400 |
| 20 | 3541034746626048000 |