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 | -1 |
| 4 | -1 |
| 5 | 4 |
| 6 | 3 |
| 7 | -147 |
| 8 | -770 |
| 9 | 15721 |
| 10 | 107475 |
| 11 | -10571326 |
| 12 | -227719699 |
| 13 | 23388067045 |
| 14 | 997369658304 |
| 15 | -266390905549461 |
| 16 | -23979310388230253 |
| 17 | 11854227262950292612 |
| 18 | 2477760824989752459951 |
| 19 | -2291696206079126389222423 |
| 20 | -973819883013544085453392378 |
| 21 | 1953283201528648806346685956669 |