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) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 4 |
| 4 | 25 |
| 5 | 174 |
| 6 | 1393 |
| 7 | 12536 |
| 8 | 125361 |
| 9 | 1378970 |
| 10 | 16547641 |
| 11 | 215119332 |
| 12 | 3011670649 |
| 13 | 45175059734 |
| 14 | 722800955745 |
| 15 | 12287616247664 |
| 16 | 221177092457953 |
| 17 | 4202364756701106 |
| 18 | 84047295134022121 |
| 19 | 1764993197814464540 |
| 20 | 38829850351918219881 |
| 21 | 893086558094119057262 |