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 | 1 |
| 2 | 2 |
| 3 | 7 |
| 4 | 32 |
| 5 | 180 |
| 6 | 1210 |
| 7 | 9520 |
| 8 | 85680 |
| 9 | 867160 |
| 10 | 9749600 |
| 11 | 120582000 |
| 12 | 1626994600 |
| 13 | 23782158400 |
| 14 | 374367193200 |
| 15 | 6314037129400 |
| 16 | 113591474796800 |
| 17 | 2171267969270400 |
| 18 | 43944509528920000 |
| 19 | 938808209417478400 |
| 20 | 21111813400597920000 |
| 21 | 498498097342637392000 |