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 | 2 |
| 3 | 9 |
| 4 | 48 |
| 5 | 330 |
| 6 | 2880 |
| 7 | 29610 |
| 8 | 362880 |
| 9 | 5148360 |
| 10 | 83462400 |
| 11 | 1535549400 |
| 12 | 31614105600 |
| 13 | 724183059600 |
| 14 | 18307441152000 |
| 15 | 507367438578000 |
| 16 | 15336404987904000 |
| 17 | 502812808754256000 |
| 18 | 17805001275629568000 |
| 19 | 678167395781763888000 |
| 20 | 27681559049033809920000 |