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 | 2 |
| 3 | 3 |
| 4 | -4 |
| 5 | -30 |
| 6 | 54 |
| 7 | 1260 |
| 8 | 3856 |
| 9 | -36288 |
| 10 | -279000 |
| 11 | 2970000 |
| 12 | 56725008 |
| 13 | 109343520 |
| 14 | -5495740992 |
| 15 | -26086263840 |
| 16 | 1293641890560 |
| 17 | 21771049466880 |
| 18 | -45508965806592 |
| 19 | -4589738336217600 |
| 20 | 10493846174810880 |
| 21 | 2423866077943511040 |
| 22 | 34328754265480012800 |
| 23 | -358930542362135546880 |