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 | 0 |
| 1 | 2 |
| 2 | 8 |
| 3 | 30 |
| 4 | 112 |
| 5 | 420 |
| 6 | 1584 |
| 7 | 6006 |
| 8 | 22880 |
| 9 | 87516 |
| 10 | 335920 |
| 11 | 1293292 |
| 12 | 4992288 |
| 13 | 19315400 |
| 14 | 74884320 |
| 15 | 290845350 |
| 16 | 1131445440 |
| 17 | 4407922860 |
| 18 | 17194993200 |
| 19 | 67156001220 |
| 20 | 262564816800 |
| 21 | 1027583214840 |
| 22 | 4025232800160 |
| 23 | 15780742227900 |
| 24 | 61915399071552 |