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 | 3 |
| 2 | 15 |
| 3 | 90 |
| 4 | 810 |
| 5 | 8100 |
| 6 | 97200 |
| 7 | 1458000 |
| 8 | 24786000 |
| 9 | 446148000 |
| 10 | 8922960000 |
| 11 | 205228080000 |
| 12 | 4925473920000 |
| 13 | 132987795840000 |
| 14 | 3856646079360000 |
| 15 | 115699382380800000 |
| 16 | 3818079618566400000 |
| 17 | 129814707031257600000 |
| 18 | 4673329453125273600000 |
| 19 | 182259848671885670400000 |