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 | 6 |
| 4 | 24 |
| 5 | 120 |
| 6 | 720 |
| 7 | 5040 |
| 8 | 40320 |
| 9 | 362880 |
| 10 | 3548160 |
| 11 | 37054080 |
| 12 | 416551680 |
| 13 | 5050368000 |
| 14 | 65944535040 |
| 15 | 924630958080 |
| 16 | 13873661706240 |
| 17 | 221978587299840 |
| 18 | 3774394191052800 |
| 19 | 67494538767237120 |
| 20 | 1276009602375352320 |
| 21 | 25429720417085030400 |