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 | 1 |
| 3 | 3 |
| 4 | 24 |
| 5 | 220 |
| 6 | 2535 |
| 7 | 35931 |
| 8 | 588028 |
| 9 | 11110212 |
| 10 | 236355885 |
| 11 | 5605425595 |
| 12 | 146586048906 |
| 13 | 4190560545678 |
| 14 | 130037568893323 |
| 15 | 4352949788266275 |
| 16 | 156362710268877960 |
| 17 | 5999465853656510056 |
| 18 | 244887352806333261753 |
| 19 | 10595948826118665719475 |
| 20 | 484448170190529051468910 |