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 | 1 |
| 2 | 0 |
| 3 | 6 |
| 4 | 4 |
| 5 | 50 |
| 6 | 66 |
| 7 | 532 |
| 8 | 1016 |
| 9 | 6876 |
| 10 | 16750 |
| 11 | 104456 |
| 12 | 303612 |
| 13 | 1821976 |
| 14 | 6067166 |
| 15 | 35857200 |
| 16 | 133160176 |
| 17 | 785514512 |
| 18 | 3192117966 |
| 19 | 18948962656 |
| 20 | 83099447300 |
| 21 | 498931946016 |
| 22 | 2336474411062 |
| 23 | 14234346694976 |
| 24 | 70598633745576 |
| 25 | 437304764440000 |
| 26 | 2282139344678726 |
| 27 | 14390600621415552 |