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 | 2 |
| 3 | 6 |
| 4 | 44 |
| 5 | 280 |
| 6 | 2100 |
| 7 | 16310 |
| 8 | 133652 |
| 9 | 1132992 |
| 10 | 9895672 |
| 11 | 88520520 |
| 12 | 808057712 |
| 13 | 7504219008 |
| 14 | 70730676392 |
| 15 | 675328163542 |
| 16 | 6521495669380 |
| 17 | 63612394972608 |
| 18 | 626076210568200 |
| 19 | 6211621325369992 |
| 20 | 62077602307372720 |
| 21 | 624488579671582880 |
| 22 | 6320044589443116720 |
| 23 | 64313288809475362888 |