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 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 1 |
| 5 | 3 |
| 6 | 13 |
| 7 | 81 |
| 8 | 577 |
| 9 | 4665 |
| 10 | 42405 |
| 11 | 427909 |
| 12 | 4745900 |
| 13 | 57382240 |
| 14 | 751185683 |
| 15 | 10584889175 |
| 16 | 159735600270 |
| 17 | 2570291022522 |
| 18 | 43928610203109 |
| 19 | 794708493674422 |
| 20 | 15171707606511701 |
| 21 | 304813398276280545 |
| 22 | 6428791672736098775 |