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 | 0 |
| 3 | -3 |
| 4 | -24 |
| 5 | -55 |
| 6 | 480 |
| 7 | 8813 |
| 8 | 61824 |
| 9 | -264591 |
| 10 | -13662720 |
| 11 | -185252771 |
| 12 | -117427200 |
| 13 | 52162650553 |
| 14 | 1214778679296 |
| 15 | 7998339208845 |
| 16 | -370278535495680 |
| 17 | -14623177924271263 |
| 18 | -202753399336206336 |
| 19 | 3863010744775239101 |
| 20 | 286065782789626920960 |
| 21 | 6603193175290504771881 |