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 | 1 |
| 3 | 4 |
| 4 | 21 |
| 5 | 160 |
| 6 | 1525 |
| 7 | 17760 |
| 8 | 243145 |
| 9 | 3833600 |
| 10 | 68373225 |
| 11 | 1361264000 |
| 12 | 29925477725 |
| 13 | 719991897600 |
| 14 | 18817847565725 |
| 15 | 530921477363200 |
| 16 | 16082605690148625 |
| 17 | 520603130117939200 |
| 18 | 17934634668874889425 |