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 | 21 |
| 5 | 54 |
| 6 | -605 |
| 7 | -8422 |
| 8 | -17815 |
| 9 | 915470 |
| 10 | 13791711 |
| 11 | -14182158 |
| 12 | -3814159811 |
| 13 | -55759417546 |
| 14 | 472583147387 |
| 15 | 33181980839114 |
| 16 | 418144112565969 |
| 17 | -10448831982433506 |
| 18 | -511822958265199817 |
| 19 | -4431070683610565086 |