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 | 4 |
| 3 | -16 |
| 4 | 74 |
| 5 | -368 |
| 6 | 1926 |
| 7 | -10455 |
| 8 | 58333 |
| 9 | -332489 |
| 10 | 1927761 |
| 11 | -11334128 |
| 12 | 67416570 |
| 13 | -404956315 |
| 14 | 2453012916 |
| 15 | -14967587873 |
| 16 | 91910798556 |
| 17 | -567566697627 |
| 18 | 3522334450512 |
| 19 | -21957276973619 |
| 20 | 137425078658354 |
| 21 | -863229921626723 |
| 22 | 5440215989173113 |
| 23 | -34388244134246836 |