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 | 30 |
| 5 | 144 |
| 6 | 758 |
| 7 | 4080 |
| 8 | 22702 |
| 9 | 128832 |
| 10 | 744300 |
| 11 | 4359972 |
| 12 | 25842414 |
| 13 | 154689912 |
| 14 | 933828324 |
| 15 | 5678696556 |
| 16 | 34754244174 |
| 17 | 213901762464 |
| 18 | 1323104558204 |
| 19 | 8220846355956 |
| 20 | 51284447272084 |
| 21 | 321095305733280 |
| 22 | 2017050339848388 |
| 23 | 12708912192988128 |
| 24 | 80296949632284814 |
| 25 | 508618518515268720 |