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 | 3 |
| 2 | 8 |
| 3 | 28 |
| 4 | 124 |
| 5 | 668 |
| 6 | 4248 |
| 7 | 31176 |
| 8 | 259488 |
| 9 | 2416032 |
| 10 | 24886080 |
| 11 | 281004480 |
| 12 | 3451887360 |
| 13 | 45832538880 |
| 14 | 654109585920 |
| 15 | 9986000371200 |
| 16 | 162391354675200 |
| 17 | 2802498609254400 |
| 18 | 51156349822771200 |
| 19 | 984775394044108800 |
| 20 | 19938798081699840000 |
| 21 | 423580563732049920000 |