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 | 0 |
| 4 | 1 |
| 5 | 5 |
| 6 | 30 |
| 7 | 210 |
| 8 | 1470 |
| 9 | 13230 |
| 10 | 132300 |
| 11 | 1455300 |
| 12 | 17671500 |
| 13 | 229729500 |
| 14 | 3216213000 |
| 15 | 48243195000 |
| 16 | 771323553000 |
| 17 | 13112500401000 |
| 18 | 236025007218000 |
| 19 | 4484475137142000 |
| 20 | 89692802577378000 |
| 21 | 1883548854124938000 |
| 22 | 41438074790748636000 |
| 23 | 953075720187218628000 |