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 | -5 |
| 5 | -149 |
| 6 | -2249 |
| 7 | -26249 |
| 8 | -251159 |
| 9 | -1443959 |
| 10 | 21646801 |
| 11 | 1209344401 |
| 12 | 35457894451 |
| 13 | 817789456771 |
| 14 | 14796993881671 |
| 15 | 137893562065351 |
| 16 | -4661597156689199 |
| 17 | -372730180154530799 |
| 18 | -16419790692323174879 |
| 19 | -559989133713039523679 |
| 20 | -14492546886670841884949 |