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 | 2 |
| 2 | 6 |
| 3 | 8 |
| 4 | 90 |
| 5 | 288 |
| 6 | 840 |
| 7 | 17280 |
| 8 | 28350 |
| 9 | 89600 |
| 10 | 598752 |
| 11 | 87091200 |
| 12 | 63063000 |
| 13 | 402361344000 |
| 14 | 5003856000 |
| 15 | 2066448384 |
| 16 | 976924698750 |
| 17 | 3766102179840000 |
| 18 | 15209113920000 |
| 19 | 5377993912811520000 |
| 20 | 1646485441080480 |
| 21 | 89903156428800000 |