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 | 1 |
| 3 | 2 |
| 4 | 21 |
| 5 | 224 |
| 6 | 3075 |
| 7 | 50364 |
| 8 | 958881 |
| 9 | 20786744 |
| 10 | 505233987 |
| 11 | 13603353928 |
| 12 | 401819713273 |
| 13 | 12917450788956 |
| 14 | 448922610588491 |
| 15 | 16770152528046332 |
| 16 | 670096317408222529 |
| 17 | 28517474585339343408 |
| 18 | 1287722135213121579203 |