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 | 5 |
| 3 | -27 |
| 4 | 171 |
| 5 | -1178 |
| 6 | 8582 |
| 7 | -65029 |
| 8 | 507317 |
| 9 | -4047608 |
| 10 | 32874104 |
| 11 | -270893586 |
| 12 | 2259210814 |
| 13 | -19032956491 |
| 14 | 161735556091 |
| 15 | -1384662302187 |
| 16 | 11931865642979 |
| 17 | -103409449621325 |
| 18 | 900778907303037 |
| 19 | -7882176975668156 |
| 20 | 69253864680597564 |
| 21 | -610717827031587856 |