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 | 3 |
| 3 | 20 |
| 4 | 186 |
| 5 | 2229 |
| 6 | 32790 |
| 7 | 572018 |
| 8 | 11541600 |
| 9 | 264370473 |
| 10 | 6776462320 |
| 11 | 192163455384 |
| 12 | 5972728750560 |
| 13 | 201906797867085 |
| 14 | 7375152706023648 |
| 15 | 289473254317393110 |
| 16 | 12149690892777901568 |
| 17 | 543010240381452000273 |
| 18 | 25746662043469525754880 |
| 19 | 1290829803802550504743036 |