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 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 2 |
| 5 | 4 |
| 6 | 12 |
| 7 | 48 |
| 8 | 240 |
| 9 | 1680 |
| 10 | 15120 |
| 11 | 181440 |
| 12 | 2903040 |
| 13 | 60963840 |
| 14 | 1706987520 |
| 15 | 63158538240 |
| 16 | 3094768373760 |
| 17 | 201159944294400 |
| 18 | 17299755209318400 |
| 19 | 1972172093862297600 |
| 20 | 297797986173206937600 |
| 21 | 59559597234641387520000 |