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 | 4 |
| 3 | 15 |
| 4 | 256 |
| 5 | 1285 |
| 6 | 5440 |
| 7 | 28123 |
| 8 | 16777216 |
| 9 | 150994953 |
| 10 | 1140868096 |
| 11 | 12465661415 |
| 12 | 73299656704 |
| 13 | 952678341901 |
| 14 | 5584872095744 |
| 15 | 56294136361779 |
| 16 | 18446744073709551616 |
| 17 | 313594649253062377489 |
| 18 | 4796153459164500459520 |
| 19 | 91477403861525991461727 |
| 20 | 1213648186380073308258304 |