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 | 9 |
| 5 | 9 |
| 6 | -73 |
| 7 | -73 |
| 8 | 697 |
| 9 | 697 |
| 10 | -7161 |
| 11 | -7161 |
| 12 | 77457 |
| 13 | 77457 |
| 14 | -868881 |
| 15 | -868881 |
| 16 | 10016241 |
| 17 | 10016241 |
| 18 | -117935473 |
| 19 | -117935473 |
| 20 | 1412307481 |
| 21 | 1412307481 |
| 22 | -17148100569 |
| 23 | -17148100569 |
| 24 | 210619695913 |
| 25 | 210619695913 |
| 26 | -2612194773481 |
| 27 | -2612194773481 |
| 28 | 32668519882017 |
| 29 | 32668519882017 |
| 30 | -411515480555553 |