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 | 1 |
| 5 | 4 |
| 6 | 20 |
| 7 | 121 |
| 8 | 862 |
| 9 | 7000 |
| 10 | 63876 |
| 11 | 646743 |
| 12 | 7195013 |
| 13 | 87239530 |
| 14 | 1145018832 |
| 15 | 16173391002 |
| 16 | 244622538903 |
| 17 | 3944538439806 |
| 18 | 67550220781672 |
| 19 | 1224347751667801 |
| 20 | 23415650750646696 |
| 21 | 471239971356764754 |