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) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 4 |
| 4 | 20 |
| 5 | 120 |
| 6 | 996 |
| 7 | 12208 |
| 8 | 241520 |
| 9 | 8171936 |
| 10 | 491317640 |
| 11 | 53489987584 |
| 12 | 10642774095040 |
| 13 | 3891541970165760 |
| 14 | 2627082058057474240 |
| 15 | 3288629181834544457216 |
| 16 | 7666328470407977450185984 |
| 17 | 33415367571344085375628748800 |
| 18 | 273361007807597539567353971109952 |