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 | 25 |
| 4 | -160 |
| 5 | 1150 |
| 6 | -8851 |
| 7 | 71345 |
| 8 | -594530 |
| 9 | 5080300 |
| 10 | -44272760 |
| 11 | 391961328 |
| 12 | -3515490820 |
| 13 | 31874449160 |
| 14 | -291676084205 |
| 15 | 2690284784605 |
| 16 | -24985250240043 |
| 17 | 233447554879855 |
| 18 | -2192862233710505 |
| 19 | 20696454624488125 |
| 20 | -196168344717398010 |
| 21 | 1866499116495323946 |