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 | 1 |
| 3 | 3 |
| 4 | 12 |
| 5 | 60 |
| 6 | 360 |
| 7 | 2016 |
| 8 | 11088 |
| 9 | 73872 |
| 10 | 602640 |
| 11 | 4411440 |
| 12 | 81677376 |
| 13 | 934435008 |
| 14 | 8100473472 |
| 15 | 104370819840 |
| 16 | 1448725616640 |
| 17 | 15823660179456 |
| 18 | 247231858514688 |
| 19 | 3703908371910912 |
| 20 | 66727356304757760 |
| 21 | 1124506454958351360 |
| 22 | 19305439846610835456 |