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 | 4 |
| 1 | 4 |
| 2 | 12 |
| 3 | 60 |
| 4 | 420 |
| 5 | 3612 |
| 6 | 35112 |
| 7 | 368940 |
| 8 | 4092660 |
| 9 | 47287812 |
| 10 | 564244824 |
| 11 | 6911705164 |
| 12 | 86538400312 |
| 13 | 1103802305800 |
| 14 | 14305263976080 |
| 15 | 187980058537740 |
| 16 | 2500329726373140 |
| 17 | 33615543407577780 |
| 18 | 456277456430657400 |
| 19 | 6246438368992478580 |
| 20 | 86175353789650193640 |