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 | 1 |
| 1 | 1 |
| 2 | 4 |
| 3 | 21 |
| 4 | 140 |
| 5 | 1130 |
| 6 | 10674 |
| 7 | 115206 |
| 8 | 1396016 |
| 9 | 18739080 |
| 10 | 275712840 |
| 11 | 4408612560 |
| 12 | 76070179272 |
| 13 | 1408041937848 |
| 14 | 27816773482848 |
| 15 | 583970117197320 |
| 16 | 12978149959718400 |
| 17 | 304310928180279360 |
| 18 | 7506092106055537344 |