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 | 0 |
| 2 | 2 |
| 3 | 30 |
| 4 | 310 |
| 5 | 2730 |
| 6 | 21980 |
| 7 | 167076 |
| 8 | 1220100 |
| 9 | 8650620 |
| 10 | 59958030 |
| 11 | 408172050 |
| 12 | 2738441706 |
| 13 | 18151701750 |
| 14 | 119100934680 |
| 15 | 774719545320 |
| 16 | 5001728701800 |
| 17 | 32081745977496 |
| 18 | 204596905143930 |
| 19 | 1298154208907430 |
| 20 | 8199305968563710 |
| 21 | 51576591659861730 |
| 22 | 323239814342259892 |
| 23 | 2019025558874685900 |