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 | -2 |
| 2 | 7 |
| 3 | -31 |
| 4 | 149 |
| 5 | -631 |
| 6 | 475 |
| 7 | 43210 |
| 8 | -844727 |
| 9 | 10960505 |
| 10 | -86569889 |
| 11 | -584746911 |
| 12 | 46302579229 |
| 13 | -1304510879686 |
| 14 | 25366896568707 |
| 15 | -277053418780891 |
| 16 | -4271166460501743 |
| 17 | 384590020131637825 |
| 18 | -14617527176248527545 |
| 19 | 380117694164438489422 |
| 20 | -5265650620303861935579 |