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 | 0 |
| 1 | 3 |
| 2 | 15 |
| 3 | 120 |
| 4 | 528 |
| 5 | 4095 |
| 6 | 17955 |
| 7 | 139128 |
| 8 | 609960 |
| 9 | 4726275 |
| 10 | 20720703 |
| 11 | 160554240 |
| 12 | 703893960 |
| 13 | 5454117903 |
| 14 | 23911673955 |
| 15 | 185279454480 |
| 16 | 812293020528 |
| 17 | 6294047334435 |
| 18 | 27594051024015 |
| 19 | 213812329916328 |
| 20 | 937385441796000 |
| 21 | 7263325169820735 |
| 22 | 31843510970040003 |
| 23 | 246739243443988680 |