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 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 12 |
| 5 | 60 |
| 6 | 340 |
| 7 | 2280 |
| 8 | 17220 |
| 9 | 151872 |
| 10 | 1459584 |
| 11 | 15624000 |
| 12 | 182318400 |
| 13 | 2316837600 |
| 14 | 31596570720 |
| 15 | 465582237120 |
| 16 | 7283287851840 |
| 17 | 121620647715840 |
| 18 | 2149774858183680 |
| 19 | 40196871701360640 |
| 20 | 790002144844738560 |
| 21 | 16364478334463078400 |
| 22 | 354458730544573132800 |