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 | 20 |
| 2 | 220 |
| 3 | 1760 |
| 4 | 11440 |
| 5 | 64064 |
| 6 | 320320 |
| 7 | 1464320 |
| 8 | 6223360 |
| 9 | 24893440 |
| 10 | 94595072 |
| 11 | 343982080 |
| 12 | 1203937280 |
| 13 | 4074864640 |
| 14 | 13388840960 |
| 15 | 42844291072 |
| 16 | 133888409600 |
| 17 | 409541017600 |
| 18 | 1228623052800 |
| 19 | 3621204787200 |
| 20 | 10501493882880 |
| 21 | 30004268236800 |