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 | 0 |
| 6 | 0 |
| 7 | 0 |
| 8 | 0 |
| 9 | 0 |
| 10 | 4 |
| 11 | 64 |
| 12 | 384 |
| 13 | 2936 |
| 14 | 10720 |
| 15 | 62664 |
| 16 | 420272 |
| 17 | 2540584 |
| 18 | 16373760 |
| 19 | 115200080 |
| 20 | 868564232 |
| 21 | 6708291360 |