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 | 2 |
| 1 | 4 |
| 2 | 12 |
| 3 | 40 |
| 4 | 140 |
| 5 | 504 |
| 6 | 1848 |
| 7 | 6864 |
| 8 | 25740 |
| 9 | 97240 |
| 10 | 369512 |
| 11 | 1410864 |
| 12 | 5408312 |
| 13 | 20801200 |
| 14 | 80233200 |
| 15 | 310235040 |
| 16 | 1202160780 |
| 17 | 4667212440 |
| 18 | 18150270600 |
| 19 | 70690527600 |
| 20 | 275693057640 |
| 21 | 1076515748880 |
| 22 | 4208197927440 |
| 23 | 16466861455200 |
| 24 | 64495207366200 |
| 25 | 252821212875504 |
| 26 | 991837065896208 |