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 | 4 |
| 2 | 40 |
| 3 | 316 |
| 4 | 2320 |
| 5 | 16564 |
| 6 | 116920 |
| 7 | 821356 |
| 8 | 5758240 |
| 9 | 40333924 |
| 10 | 282416200 |
| 11 | 1977149596 |
| 12 | 13840755760 |
| 13 | 96887416084 |
| 14 | 678218289880 |
| 15 | 4747547161036 |
| 16 | 33232887522880 |
| 17 | 232630384847044 |
| 18 | 1628413210489960 |
| 19 | 11398894023111676 |
| 20 | 79792262810827600 |
| 21 | 558545853622930804 |
| 22 | 3909821017201928440 |