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 | 0 |
| 4 | 24 |
| 5 | -55 |
| 6 | 630 |
| 7 | -2723 |
| 8 | 30968 |
| 9 | -294327 |
| 10 | 3047320 |
| 11 | -30255379 |
| 12 | 387690732 |
| 13 | -5565964391 |
| 14 | 77090414492 |
| 15 | -1114263777885 |
| 16 | 18473122449616 |
| 17 | -331776991760303 |
| 18 | 6106973926830192 |
| 19 | -112710455017397639 |
| 20 | 2233663985151902860 |
| 21 | -50049383051597936559 |