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 | 1 |
| 2 | 6 |
| 3 | 30 |
| 4 | 180 |
| 5 | 1455 |
| 6 | 15666 |
| 7 | 213500 |
| 8 | 3521736 |
| 9 | 68101245 |
| 10 | 1508916310 |
| 11 | 37661140506 |
| 12 | 1045012524348 |
| 13 | 31900040161899 |
| 14 | 1062139933257690 |
| 15 | 38299757176168440 |
| 16 | 1486670929792295696 |
| 17 | 61800664096000744569 |
| 18 | 2738952078516469743678 |
| 19 | 128909373997071187219990 |