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 | 3 |
| 4 | -20 |
| 5 | -320 |
| 6 | -2274 |
| 7 | 5474 |
| 8 | 487432 |
| 9 | 8358480 |
| 10 | 37944240 |
| 11 | -2286868848 |
| 12 | -81319780200 |
| 13 | -1139790073968 |
| 14 | 18382692073032 |
| 15 | 1570867988794680 |
| 16 | 42704382709868736 |
| 17 | 55662087673489920 |
| 18 | -49662902468183117760 |
| 19 | -2360239974764654675904 |
| 20 | -38098700311039336972800 |