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 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 4 |
| 5 | -10 |
| 6 | -130 |
| 7 | -840 |
| 8 | -5880 |
| 9 | -36960 |
| 10 | -142800 |
| 11 | 184800 |
| 12 | 12843600 |
| 13 | 229429200 |
| 14 | 3035432400 |
| 15 | 31615584000 |
| 16 | 258306048000 |
| 17 | 943422480000 |
| 18 | -26673126480000 |
| 19 | -902769547680000 |
| 20 | -18345450483360000 |
| 21 | -300501672831360000 |
| 22 | -3983084426280960000 |