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 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 3 |
| 6 | 19 |
| 7 | 120 |
| 8 | 861 |
| 9 | 7000 |
| 10 | 63875 |
| 11 | 646742 |
| 12 | 7195012 |
| 13 | 87239530 |
| 14 | 1145018831 |
| 15 | 16173391001 |
| 16 | 244622538902 |
| 17 | 3944538439805 |
| 18 | 67550220781671 |
| 19 | 1224347751667801 |
| 20 | 23415650750646695 |
| 21 | 471239971356764753 |