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 | 20 |
| 3 | 112 |
| 4 | 656 |
| 5 | 3904 |
| 6 | 23360 |
| 7 | 140032 |
| 8 | 839936 |
| 9 | 5039104 |
| 10 | 30233600 |
| 11 | 181399552 |
| 12 | 1088393216 |
| 13 | 6530351104 |
| 14 | 39182090240 |
| 15 | 235092508672 |
| 16 | 1410554986496 |
| 17 | 8463329787904 |
| 18 | 50779978465280 |
| 19 | 304679870267392 |
| 20 | 1828079220555776 |