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 | 28 |
| 5 | -30 |
| 6 | 888 |
| 7 | -1260 |
| 8 | 51728 |
| 9 | -196560 |
| 10 | 5293080 |
| 11 | -22286880 |
| 12 | 710229408 |
| 13 | -4851269280 |
| 14 | 138348035616 |
| 15 | -1091188098000 |
| 16 | 36482139114240 |
| 17 | -379928382462720 |
| 18 | 11812558481332992 |
| 19 | -137793570801143040 |
| 20 | 4609972759421554560 |
| 21 | -67292912045817561600 |