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 | 5 |
| 4 | 20 |
| 5 | 84 |
| 6 | 424 |
| 7 | 2680 |
| 8 | 20544 |
| 9 | 182336 |
| 10 | 1816448 |
| 11 | 19963008 |
| 12 | 239511040 |
| 13 | 3113532928 |
| 14 | 43589194752 |
| 15 | 653837290496 |
| 16 | 10461395173376 |
| 17 | 177843714539520 |
| 18 | 3201186853912576 |
| 19 | 60822550206644224 |
| 20 | 1216451004093038592 |
| 21 | 25545471085864681472 |
| 22 | 562000363888824811520 |