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 | 0 |
| 2 | 0 |
| 3 | 4 |
| 4 | 24 |
| 5 | 100 |
| 6 | 360 |
| 7 | 1204 |
| 8 | 3864 |
| 9 | 12100 |
| 10 | 37320 |
| 11 | 114004 |
| 12 | 346104 |
| 13 | 1046500 |
| 14 | 3155880 |
| 15 | 9500404 |
| 16 | 28566744 |
| 17 | 85831300 |
| 18 | 257756040 |
| 19 | 773792404 |
| 20 | 2322425784 |
| 21 | 6969374500 |
| 22 | 20912317800 |
| 23 | 62745342004 |
| 24 | 188252803224 |
| 25 | 564791964100 |
| 26 | 1694443001160 |
| 27 | 5083463221204 |
| 28 | 15250658099064 |