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 | 1 |
| 4 | 15 |
| 5 | 252 |
| 6 | 5005 |
| 7 | 116280 |
| 8 | 3108105 |
| 9 | 94143280 |
| 10 | 3190187286 |
| 11 | 119653565850 |
| 12 | 4922879481520 |
| 13 | 220495674290430 |
| 14 | 10682005290753420 |
| 15 | 556608279578340080 |
| 16 | 31044058215401404845 |
| 17 | 1845382436487682488000 |
| 18 | 116475817125419611477660 |
| 19 | 7779819801401934344268210 |