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 | 7 |
| 2 | 42 |
| 3 | 252 |
| 4 | 1512 |
| 5 | 9072 |
| 6 | 54432 |
| 7 | 326592 |
| 8 | 1959552 |
| 9 | 11757312 |
| 10 | 70543872 |
| 11 | 423263232 |
| 12 | 2539579392 |
| 13 | 15237476331 |
| 14 | 91424857860 |
| 15 | 548549146425 |
| 16 | 3291294874140 |
| 17 | 19747769218380 |
| 18 | 118486615151520 |
| 19 | 710919689956560 |
| 20 | 4265518134024000 |