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 | -6 |
| 4 | 12 |
| 5 | 0 |
| 6 | -240 |
| 7 | 2520 |
| 8 | -18480 |
| 9 | 60480 |
| 10 | 937440 |
| 11 | -21621600 |
| 12 | 220207680 |
| 13 | -311351040 |
| 14 | -34490776320 |
| 15 | 724669545600 |
| 16 | -6625031212800 |
| 17 | -49471604582400 |
| 18 | 3116728731916800 |
| 19 | -58942964451571200 |
| 20 | 335128094882380800 |
| 21 | 15732203147781120000 |
| 22 | -600651799248659558400 |