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 | 4 |
| 2 | 26 |
| 3 | 240 |
| 4 | 2904 |
| 5 | 43680 |
| 6 | 786960 |
| 7 | 16531200 |
| 8 | 396789120 |
| 9 | 10713669120 |
| 10 | 321413702400 |
| 11 | 10606692096000 |
| 12 | 381841394457600 |
| 13 | 14891820610867200 |
| 14 | 625456552834713600 |
| 15 | 28145546185236480000 |
| 16 | 1350986237814140928000 |
| 17 | 68900298484208615424000 |
| 18 | 3720616124549638938624000 |