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 | 2 |
| 2 | 21 |
| 3 | 312 |
| 4 | 5880 |
| 5 | 133920 |
| 6 | 3575880 |
| 7 | 109549440 |
| 8 | 3788104320 |
| 9 | 145957593600 |
| 10 | 6201593798400 |
| 11 | 288084016281600 |
| 12 | 14525808782284800 |
| 13 | 790129980896256000 |
| 14 | 46120599397192320000 |
| 15 | 2875600728738017280000 |
| 16 | 190740227037467627520000 |
| 17 | 13411608375592258191360000 |