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 | 1 |
| 3 | -3 |
| 4 | 20 |
| 5 | -120 |
| 6 | 976 |
| 7 | -8568 |
| 8 | 88640 |
| 9 | -1011840 |
| 10 | 12933376 |
| 11 | -180964608 |
| 12 | 2767631360 |
| 13 | -45799004160 |
| 14 | 816582578176 |
| 15 | -15594628021248 |
| 16 | 317710534983680 |
| 17 | -6876762625966080 |
| 18 | 157606194409701376 |
| 19 | -3812723805066559488 |