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 | 6 |
| 2 | 30 |
| 3 | 144 |
| 4 | 684 |
| 5 | 3240 |
| 6 | 15336 |
| 7 | 72576 |
| 8 | 343440 |
| 9 | 1625184 |
| 10 | 7690464 |
| 11 | 36391680 |
| 12 | 172207296 |
| 13 | 814893696 |
| 14 | 3856118400 |
| 15 | 18247348224 |
| 16 | 86347378944 |
| 17 | 408600184320 |
| 18 | 1933516832256 |
| 19 | 9149499887616 |
| 20 | 43295898332160 |
| 21 | 204878390667264 |
| 22 | 969494954010624 |
| 23 | 4587699380060160 |