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 | 2 |
| 3 | 8 |
| 4 | 30 |
| 5 | 156 |
| 6 | 900 |
| 7 | 6192 |
| 8 | 47904 |
| 9 | 422928 |
| 10 | 4138848 |
| 11 | 44864640 |
| 12 | 531227520 |
| 13 | 6836927040 |
| 14 | 94891046400 |
| 15 | 1413494219520 |
| 16 | 22481104677120 |
| 17 | 380261238681600 |
| 18 | 6814832064422400 |
| 19 | 128991143627965440 |
| 20 | 2571187988206540800 |
| 21 | 53834676521793638400 |
| 22 | 1181214133296983654400 |