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 | 3 |
| 2 | 15 |
| 3 | 73 |
| 4 | 354 |
| 5 | 1716 |
| 6 | 8318 |
| 7 | 40320 |
| 8 | 195444 |
| 9 | 947380 |
| 10 | 4592256 |
| 11 | 22260144 |
| 12 | 107902088 |
| 13 | 523036176 |
| 14 | 2535324816 |
| 15 | 12289536016 |
| 16 | 59571339552 |
| 17 | 288761470848 |
| 18 | 1399719859808 |
| 19 | 6784893012864 |
| 20 | 32888561860032 |
| 21 | 159421452802624 |
| 22 | 772767131681280 |
| 23 | 3745851196992000 |