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 | 3 |
| 3 | -6 |
| 4 | 20 |
| 5 | -50 |
| 6 | 175 |
| 7 | -490 |
| 8 | 1764 |
| 9 | -5292 |
| 10 | 19404 |
| 11 | -60984 |
| 12 | 226512 |
| 13 | -736164 |
| 14 | 2760615 |
| 15 | -9202050 |
| 16 | 34763300 |
| 17 | -118195220 |
| 18 | 449141836 |
| 19 | -1551580888 |
| 20 | 5924217936 |
| 21 | -20734762776 |
| 22 | 79483257308 |
| 23 | -281248448936 |
| 24 | 1081724803600 |
| 25 | -3863302870000 |
| 26 | 14901311070000 |
| 27 | -53644719852000 |