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 | 1 |
| 3 | 6 |
| 4 | 30 |
| 5 | 160 |
| 6 | 975 |
| 7 | 6846 |
| 8 | 54796 |
| 9 | 493200 |
| 10 | 4932045 |
| 11 | 54252550 |
| 12 | 651030666 |
| 13 | 8463398736 |
| 14 | 118487582395 |
| 15 | 1777313736030 |
| 16 | 28437019776600 |
| 17 | 483429336202336 |
| 18 | 8701728051642201 |
| 19 | 165332832981201990 |
| 20 | 3306656659624039990 |
| 21 | 69439789852104840000 |