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 | 2 |
| 2 | 9 |
| 3 | 40 |
| 4 | 212 |
| 5 | 1248 |
| 6 | 8400 |
| 7 | 63576 |
| 8 | 540858 |
| 9 | 5132564 |
| 10 | 53952742 |
| 11 | 623324184 |
| 12 | 7855144818 |
| 13 | 107224120980 |
| 14 | 1575511525794 |
| 15 | 24784246515256 |
| 16 | 415435624535225 |
| 17 | 7389692971336602 |
| 18 | 138992875726543381 |
| 19 | 2755750468146310688 |
| 20 | 57433108983590606292 |