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 | 1 |
| 2 | 2 |
| 3 | 4 |
| 4 | 24 |
| 5 | 144 |
| 6 | 480 |
| 7 | 4320 |
| 8 | 40320 |
| 9 | 282240 |
| 10 | 4354560 |
| 11 | 36288000 |
| 12 | 319334400 |
| 13 | 6706022400 |
| 14 | 74724249600 |
| 15 | 1046139494400 |
| 16 | 20922789888000 |
| 17 | 376610217984000 |
| 18 | 4979623993344000 |
| 19 | 115242726703104000 |
| 20 | 2919482409811968000 |
| 21 | 29194824098119680000 |