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 | 0 |
| 2 | 1 |
| 3 | 3 |
| 4 | 9 |
| 5 | 105 |
| 6 | 315 |
| 7 | 4095 |
| 8 | 11025 |
| 9 | 348705 |
| 10 | 1545075 |
| 11 | 17931375 |
| 12 | 93087225 |
| 13 | 3764185425 |
| 14 | 45589819275 |
| 15 | 1060569885375 |
| 16 | 15877899662625 |
| 17 | 900941666625 |
| 18 | 5722531807867875 |
| 19 | 90088576482279375 |
| 20 | 1688777976676415625 |
| 21 | 18148954872023600625 |
| 22 | 320586579951629866875 |
| 23 | 11054393914490520969375 |