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 | 4 |
| 3 | 18 |
| 4 | 108 |
| 5 | 840 |
| 6 | 7680 |
| 7 | 82320 |
| 8 | 1009680 |
| 9 | 13910400 |
| 10 | 213071040 |
| 11 | 3589850880 |
| 12 | 65975152320 |
| 13 | 1313624632320 |
| 14 | 28166959941120 |
| 15 | 647099547494400 |
| 16 | 15857424488505600 |
| 17 | 412878579034521600 |
| 18 | 11382450106662835200 |
| 19 | 331230511848421785600 |
| 20 | 10146149192841050188800 |