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 | 6 |
| 3 | 30 |
| 4 | 192 |
| 5 | 1450 |
| 6 | 12960 |
| 7 | 133574 |
| 8 | 1550976 |
| 9 | 20055186 |
| 10 | 285903360 |
| 11 | 4452231982 |
| 12 | 75186726912 |
| 13 | 1368588922298 |
| 14 | 26709799753728 |
| 15 | 556339845854550 |
| 16 | 12318065768693760 |
| 17 | 288894650033594914 |
| 18 | 7154212267816648704 |
| 19 | 186545064693433665854 |
| 20 | 5108590743587243950080 |