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 | 0 |
| 2 | 0 |
| 3 | 1 |
| 4 | 6 |
| 5 | 20 |
| 6 | 134 |
| 7 | 915 |
| 8 | 7324 |
| 9 | 65784 |
| 10 | 657180 |
| 11 | 7223637 |
| 12 | 86637650 |
| 13 | 1125842556 |
| 14 | 15757002706 |
| 15 | 236298742375 |
| 16 | 3780061394232 |
| 17 | 64251145312880 |
| 18 | 1156374220457784 |
| 19 | 21968796934412649 |
| 20 | 439337048505773790 |
| 21 | 9225384943965382564 |
| 22 | 202945418255342821470 |