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 | 6 |
| 2 | 30 |
| 3 | 135 |
| 4 | 600 |
| 5 | 2640 |
| 6 | 11610 |
| 7 | 51000 |
| 8 | 224040 |
| 9 | 984060 |
| 10 | 4322400 |
| 11 | 18985440 |
| 12 | 83390760 |
| 13 | 366280800 |
| 14 | 1608831840 |
| 15 | 7066542960 |
| 16 | 31038691200 |
| 17 | 136332618240 |
| 18 | 598819808160 |
| 19 | 2630222793600 |
| 20 | 11552844224640 |
| 21 | 50744069991360 |