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 | 2 |
| 2 | 4 |
| 3 | 9 |
| 4 | 40 |
| 5 | 192 |
| 6 | 1032 |
| 7 | 7824 |
| 8 | 62496 |
| 9 | 530712 |
| 10 | 5619456 |
| 11 | 61710336 |
| 12 | 707802624 |
| 13 | 9591229440 |
| 14 | 133983590400 |
| 15 | 1938416832000 |
| 16 | 32061464064000 |
| 17 | 544216485888000 |
| 18 | 9509523337728000 |
| 19 | 185772505605120000 |
| 20 | 3711395156281344000 |