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 | 3 |
| 4 | 28 |
| 5 | 305 |
| 6 | 3846 |
| 7 | 57337 |
| 8 | 998600 |
| 9 | 20036529 |
| 10 | 456403690 |
| 11 | 11647754921 |
| 12 | 329290975212 |
| 13 | 10214585950153 |
| 14 | 344897398385918 |
| 15 | 12590837785019145 |
| 16 | 494101941398352016 |
| 17 | 20740772742716097377 |
| 18 | 927276395603713539282 |
| 19 | 43987299891665164562377 |
| 20 | 2206610456287703987567540 |