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) |
|---|---|
| 1 | 2 |
| 2 | 12 |
| 3 | 56 |
| 4 | 240 |
| 5 | 990 |
| 6 | 4004 |
| 7 | 16016 |
| 8 | 63648 |
| 9 | 251940 |
| 10 | 994840 |
| 11 | 3922512 |
| 12 | 15452320 |
| 13 | 60843510 |
| 14 | 239519700 |
| 15 | 942871200 |
| 16 | 3711935040 |
| 17 | 14615744220 |
| 18 | 57562286760 |
| 19 | 226760523600 |
| 20 | 893550621600 |
| 21 | 3522078700140 |
| 22 | 13887053160552 |