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 | 0 |
| 2 | -1 |
| 3 | 0 |
| 4 | -6 |
| 5 | 8 |
| 6 | -150 |
| 7 | 448 |
| 8 | -7560 |
| 9 | 38432 |
| 10 | -642600 |
| 11 | 4827328 |
| 12 | -83392848 |
| 13 | 846371264 |
| 14 | -15413462064 |
| 15 | 198308799232 |
| 16 | -3850826179200 |
| 17 | 59939510237696 |
| 18 | -1248952432920192 |
| 19 | 22723443584373760 |
| 20 | -509532711855338240 |
| 21 | 10564033699974222848 |
| 22 | -255033199091475264768 |