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 | 1 |
| 2 | 1 |
| 3 | 6 |
| 4 | 39 |
| 5 | 390 |
| 6 | 4815 |
| 7 | 73080 |
| 8 | 1304415 |
| 9 | 26847450 |
| 10 | 625528575 |
| 11 | 16279193700 |
| 12 | 468022452975 |
| 13 | 14731683916950 |
| 14 | 503880434632575 |
| 15 | 18609309606888000 |
| 16 | 738057377647965375 |
| 17 | 31286068076704691250 |
| 18 | 1411602439003747365375 |
| 19 | 67543694966494692445500 |
| 20 | 3416288904242387117319375 |