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 | 18 |
| 4 | 120 |
| 5 | 840 |
| 6 | 9360 |
| 7 | 115920 |
| 8 | 1491840 |
| 9 | 22861440 |
| 10 | 395539200 |
| 11 | 7304774400 |
| 12 | 148011494400 |
| 13 | 3281639961600 |
| 14 | 77850214041600 |
| 15 | 1975895970048000 |
| 16 | 53666956062720000 |
| 17 | 1547595999645696000 |
| 18 | 47204701332332544000 |