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 | -9 |
| 4 | 33 |
| 5 | -241 |
| 6 | 1761 |
| 7 | -15929 |
| 8 | 161473 |
| 9 | -1853281 |
| 10 | 23584321 |
| 11 | -330371049 |
| 12 | 5047404513 |
| 13 | -83546832721 |
| 14 | 1489242229281 |
| 15 | -28442492633369 |
| 16 | 579425286625153 |
| 17 | -12541705195066561 |
| 18 | 287434687338368641 |
| 19 | -6953491183101074889 |
| 20 | 177069197398959999393 |
| 21 | -4734481603905334522801 |