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 | 1 |
| 2 | 4 |
| 3 | 28 |
| 4 | 280 |
| 5 | 3640 |
| 6 | 58240 |
| 7 | 1106560 |
| 8 | 24344320 |
| 9 | 608608000 |
| 10 | 17041024000 |
| 11 | 528271744000 |
| 12 | 17961239296000 |
| 13 | 664565853952000 |
| 14 | 26582634158080000 |
| 15 | 1143053268797440000 |
| 16 | 52580450364682240000 |
| 17 | 2576442067869429760000 |
| 18 | 133974987529210347520000 |
| 19 | 7368624314106569113600000 |