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) |
|---|---|
| 1 | 0 |
| 2 | 2 |
| 3 | 12 |
| 4 | 72 |
| 5 | 480 |
| 6 | 4320 |
| 7 | 35280 |
| 8 | 322560 |
| 9 | 3265920 |
| 10 | 39916800 |
| 11 | 479001600 |
| 12 | 6706022400 |
| 13 | 93405312000 |
| 14 | 1482030950400 |
| 15 | 24845812992000 |
| 16 | 418455797760000 |
| 17 | 7469435990016000 |
| 18 | 147254595231744000 |
| 19 | 2919482409811968000 |
| 20 | 63255452212592640000 |
| 21 | 1430546380807864320000 |