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 | 150 |
| 4 | 750 |
| 5 | 3735 |
| 6 | 18600 |
| 7 | 92640 |
| 8 | 461400 |
| 9 | 2298000 |
| 10 | 11445210 |
| 11 | 57003000 |
| 12 | 283904040 |
| 13 | 1413987000 |
| 14 | 7042377000 |
| 15 | 35074632060 |
| 16 | 174689570400 |
| 17 | 870043225440 |
| 18 | 4333259349600 |
| 19 | 21581843340000 |
| 20 | 107488595621160 |
| 21 | 535348070440800 |