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 | 4 |
| 2 | 28 |
| 3 | 224 |
| 4 | 1888 |
| 5 | 16320 |
| 6 | 143040 |
| 7 | 1264128 |
| 8 | 11230720 |
| 9 | 100124672 |
| 10 | 894785536 |
| 11 | 8010072064 |
| 12 | 71794294784 |
| 13 | 644079468544 |
| 14 | 5782109208576 |
| 15 | 51934915067904 |
| 16 | 466666751655936 |
| 17 | 4194593964294144 |
| 18 | 37711993926844416 |
| 19 | 339119962067042304 |
| 20 | 3049961818869989376 |
| 21 | 27434013235435536384 |