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 | 0 |
| 2 | 1 |
| 3 | 6 |
| 4 | 30 |
| 5 | 130 |
| 6 | 570 |
| 7 | 2436 |
| 8 | 10696 |
| 9 | 47160 |
| 10 | 213660 |
| 11 | 981640 |
| 12 | 4625016 |
| 13 | 22171656 |
| 14 | 108766840 |
| 15 | 543350640 |
| 16 | 2772404160 |
| 17 | 14402353216 |
| 18 | 76294507536 |
| 19 | 411229473120 |
| 20 | 2257073089120 |
| 21 | 12595032754080 |
| 22 | 71481175794336 |
| 23 | 412117251151936 |
| 24 | 2413922299708800 |
| 25 | 14352066564086400 |