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 | 2 |
| 4 | 3 |
| 5 | 8 |
| 6 | 90 |
| 7 | 384 |
| 8 | 2940 |
| 9 | 18864 |
| 10 | 232848 |
| 11 | 1919520 |
| 12 | 23364000 |
| 13 | 261282240 |
| 14 | 3486637440 |
| 15 | 48900116160 |
| 16 | 746747164800 |
| 17 | 11559784320000 |
| 18 | 201817271416320 |
| 19 | 3580457619916800 |
| 20 | 68121866659875840 |
| 21 | 1366946563510886400 |
| 22 | 28802183294533017600 |
| 23 | 627950275273991577600 |