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 | 0 |
| 3 | 3 |
| 4 | 6 |
| 5 | 20 |
| 6 | 0 |
| 7 | -126 |
| 8 | -1260 |
| 9 | 18360 |
| 10 | 335160 |
| 11 | 4546080 |
| 12 | 26302320 |
| 13 | -59501520 |
| 14 | -5703994296 |
| 15 | -58549768200 |
| 16 | 371346066000 |
| 17 | 34962417322560 |
| 18 | 746101280831040 |
| 19 | 8059680118183680 |
| 20 | -93772611412099200 |
| 21 | -5613314502242643840 |
| 22 | -110940169654432087200 |