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 | 0 |
| 1 | 1 |
| 2 | -4 |
| 3 | 17 |
| 4 | -85 |
| 5 | 499 |
| 6 | -3388 |
| 7 | 26200 |
| 8 | -227708 |
| 9 | 2199276 |
| 10 | -23382216 |
| 11 | 271461816 |
| 12 | -3418002432 |
| 13 | 46399476096 |
| 14 | -675622445184 |
| 15 | 10504980616320 |
| 16 | -173726527230720 |
| 17 | 3045008035203840 |
| 18 | -56389237652344320 |
| 19 | 1100174877158791680 |
| 20 | -22556707790402304000 |
| 21 | 484876713643386624000 |