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 | 1 |
| 2 | 0 |
| 3 | 0 |
| 4 | 2 |
| 5 | 10 |
| 6 | 4 |
| 7 | 28 |
| 8 | 20 |
| 9 | 56 |
| 10 | 72 |
| 11 | 288 |
| 12 | 1304 |
| 13 | 6368 |
| 14 | 22884 |
| 15 | 125864 |
| 16 | 755412 |
| 17 | 4565572 |
| 18 | 29862256 |
| 19 | 207238124 |
| 20 | 1540506028 |
| 21 | 11774180220 |