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 | 12 |
| 4 | 120 |
| 5 | 1200 |
| 6 | 14400 |
| 7 | 191520 |
| 8 | 2862720 |
| 9 | 47174400 |
| 10 | 852768000 |
| 11 | 16765056000 |
| 12 | 356377190400 |
| 13 | 8144943206400 |
| 14 | 199202395392000 |
| 15 | 5191467240960000 |
| 16 | 143634952581120000 |
| 17 | 4204936774950912000 |
| 18 | 129865748246986752000 |
| 19 | 4219868533182382080000 |
| 20 | 143918318293689139200000 |