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 | 11 |
| 4 | -23 |
| 5 | -101 |
| 6 | 991 |
| 7 | -1849 |
| 8 | -24751 |
| 9 | 220823 |
| 10 | -174689 |
| 11 | -10924541 |
| 12 | 87639289 |
| 13 | 105372851 |
| 14 | -7496679553 |
| 15 | 52397291519 |
| 16 | 238887991201 |
| 17 | -7313210597969 |
| 18 | 41947208776639 |
| 19 | 440627548672763 |
| 20 | -9537975555701239 |
| 21 | 39732691614159179 |
| 22 | 916052993052974239 |