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 | -2 |
| 3 | 2 |
| 4 | 40 |
| 5 | 104 |
| 6 | -1232 |
| 7 | -13168 |
| 8 | 16000 |
| 9 | 1483904 |
| 10 | 9695488 |
| 11 | -151161088 |
| 12 | -3287997440 |
| 13 | 146760704 |
| 14 | 866038110208 |
| 15 | 10263094740992 |
| 16 | -169941494497280 |
| 17 | -6324725967978496 |
| 18 | -15215847186563072 |
| 19 | 2895126258819203072 |
| 20 | 54295929047166484480 |