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 | 2 |
| 4 | -2 |
| 5 | 18 |
| 6 | -128 |
| 7 | 740 |
| 8 | -3204 |
| 9 | -6076 |
| 10 | 210304 |
| 11 | -1097064 |
| 12 | -29284760 |
| 13 | 398231768 |
| 14 | 792490752 |
| 15 | -124480674448 |
| 16 | 1471405254928 |
| 17 | -2684728872720 |
| 18 | -64686947480576 |
| 19 | -626709774748384 |
| 20 | -10524779012515104 |
| 21 | 689522178752789024 |
| 22 | 34910956277827256320 |