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) |
|---|---|
| 3 | 0 |
| 4 | 2 |
| 5 | 6 |
| 6 | 18 |
| 7 | 62 |
| 8 | 210 |
| 9 | 728 |
| 10 | 2570 |
| 11 | 9198 |
| 12 | 33288 |
| 13 | 121574 |
| 14 | 447394 |
| 15 | 1657008 |
| 16 | 6170930 |
| 17 | 23091222 |
| 18 | 86767016 |
| 19 | 327235610 |
| 20 | 1238188770 |
| 21 | 4698767640 |