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 | 5 |
| 3 | 17 |
| 4 | 74 |
| 5 | 394 |
| 6 | 2484 |
| 7 | 18108 |
| 8 | 149904 |
| 9 | 1389456 |
| 10 | 14257440 |
| 11 | 160460640 |
| 12 | 1965444480 |
| 13 | 26029779840 |
| 14 | 370643938560 |
| 15 | 5646837369600 |
| 16 | 91657072281600 |
| 17 | 1579093018675200 |
| 18 | 28779361764249600 |
| 19 | 553210247226470400 |
| 20 | 11185850044938240000 |
| 21 | 237335752951879680000 |