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 | 0 |
| 1 | 4 |
| 2 | 24 |
| 3 | 140 |
| 4 | 816 |
| 5 | 4756 |
| 6 | 27720 |
| 7 | 161564 |
| 8 | 941664 |
| 9 | 5488420 |
| 10 | 31988856 |
| 11 | 186444716 |
| 12 | 1086679440 |
| 13 | 6333631924 |
| 14 | 36915112104 |
| 15 | 215157040700 |
| 16 | 1254027132096 |
| 17 | 7309005751876 |
| 18 | 42600007379160 |
| 19 | 248291038523084 |
| 20 | 1447146223759344 |
| 21 | 8434586304032980 |