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 | 0 |
| 2 | -2 |
| 3 | -3 |
| 4 | 28 |
| 5 | 150 |
| 6 | -714 |
| 7 | -10920 |
| 8 | 13392 |
| 9 | 1129464 |
| 10 | 3694680 |
| 11 | -150143400 |
| 12 | -1515256104 |
| 13 | 22631946480 |
| 14 | 525582087408 |
| 15 | -2756199995640 |
| 16 | -192774443051520 |
| 17 | -525316900812480 |
| 18 | 75951597634314048 |
| 19 | 926307802605928320 |
| 20 | -30597152030347651200 |
| 21 | -833744424171043728000 |