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 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 14 |
| 5 | 80 |
| 6 | 468 |
| 7 | 2268 |
| 8 | 10224 |
| 9 | 313632 |
| 10 | 9849600 |
| 11 | 21954240 |
| 12 | -8894136960 |
| 13 | -105857556480 |
| 14 | 20609598562560 |
| 15 | 650835095904000 |
| 16 | -80028503341516800 |
| 17 | -5018759207362252800 |
| 18 | 503681435808239001600 |
| 19 | 56090762228110443724800 |