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 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 24 |
| 5 | 60 |
| 6 | 840 |
| 7 | 10290 |
| 8 | 80976 |
| 9 | 847224 |
| 10 | 13306320 |
| 11 | 190271070 |
| 12 | 2677088040 |
| 13 | 46082426676 |
| 14 | 874515884424 |
| 15 | 16582066303530 |
| 16 | 336875275380000 |
| 17 | 7539189088358640 |
| 18 | 176554878235711776 |
| 19 | 4295134487197296054 |
| 20 | 111114287924643309240 |
| 21 | 3036073975138066955820 |