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 | 6 |
| 4 | 20 |
| 5 | 110 |
| 6 | 612 |
| 7 | 4970 |
| 8 | 39600 |
| 9 | 337680 |
| 10 | 3298900 |
| 11 | 39916800 |
| 12 | 442155168 |
| 13 | 6151996372 |
| 14 | 83387930692 |
| 15 | 1282826630160 |
| 16 | 19089488332800 |
| 17 | 355148307803520 |
| 18 | 5427568925856000 |
| 19 | 119931789135468100 |
| 20 | 2432901890279317572 |
| 21 | 49902667163053013232 |
| 22 | 1073067539495604750240 |