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 | 6 |
| 4 | -36 |
| 5 | 210 |
| 6 | -630 |
| 7 | -5376 |
| 8 | 153048 |
| 9 | -2194296 |
| 10 | 22190760 |
| 11 | -93956544 |
| 12 | -2677330656 |
| 13 | 97821857952 |
| 14 | -2019503487456 |
| 15 | 27899293618944 |
| 16 | -98409183995520 |
| 17 | -9548919666829440 |
| 18 | 410311098024923520 |
| 19 | -10652005874894469120 |
| 20 | 176525303194482117120 |
| 21 | -46197517147757867520 |