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 | 0 |
| 3 | 2 |
| 4 | 8 |
| 5 | 20 |
| 6 | 80 |
| 7 | 350 |
| 8 | 1232 |
| 9 | 5768 |
| 10 | 31040 |
| 11 | 142010 |
| 12 | 776600 |
| 13 | 4874012 |
| 14 | 27027728 |
| 15 | 168369110 |
| 16 | 1191911840 |
| 17 | 7678566800 |
| 18 | 53474964992 |
| 19 | 418199988338 |
| 20 | 3044269834280 |
| 21 | 23364756531620 |
| 22 | 199008751634000 |
| 23 | 1605461415071822 |