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 | -1 |
| 4 | -23 |
| 5 | 119 |
| 6 | -359 |
| 7 | -4201 |
| 8 | 58801 |
| 9 | -359857 |
| 10 | -2121839 |
| 11 | 74851919 |
| 12 | -784376999 |
| 13 | -1072414201 |
| 14 | 192596540137 |
| 15 | -3167640042841 |
| 16 | 9241215940321 |
| 17 | 860635956717599 |
| 18 | -21290802661288799 |
| 19 | 157132294452113183 |
| 20 | 5980504635868174921 |
| 21 | -220612220726623344361 |