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 | 1 |
| 2 | 0 |
| 3 | -6 |
| 4 | -36 |
| 5 | -120 |
| 6 | 240 |
| 7 | 8400 |
| 8 | 82320 |
| 9 | 362880 |
| 10 | -3507840 |
| 11 | -103783680 |
| 12 | -1268688960 |
| 13 | -4843238400 |
| 14 | 175429013760 |
| 15 | 5052189542400 |
| 16 | 68016191443200 |
| 17 | 55329155481600 |
| 18 | -23284682272051200 |
| 19 | -668640423164313600 |
| 20 | -9013925405784499200 |
| 21 | 57340797108269875200 |