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 | 1 |
| 3 | 3 |
| 4 | 6 |
| 5 | 30 |
| 6 | 300 |
| 7 | 2100 |
| 8 | 11760 |
| 9 | 105840 |
| 10 | 1421280 |
| 11 | 15634080 |
| 12 | 147692160 |
| 13 | 1919998080 |
| 14 | 33106993920 |
| 15 | 496604908800 |
| 16 | 6638004172800 |
| 17 | 112846070937600 |
| 18 | 2386916704972800 |
| 19 | 45351417394483200 |
| 20 | 785383247480832000 |
| 21 | 16493048197097472000 |
| 22 | 413938002507853824000 |