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) |
|---|---|
| 1 | 0 |
| 2 | 3 |
| 3 | 10 |
| 4 | 21 |
| 5 | 3960 |
| 6 | 77220 |
| 7 | 490089600 |
| 8 | 1523733120 |
| 9 | 2075793350400 |
| 10 | 50710801232931840000 |
| 11 | 3144069676441774080000 |
| 12 | 19348101737674447004467200000 |
| 13 | 137500509682406403378413568000000 |