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 | 0 |
| 3 | 0 |
| 4 | 1 |
| 5 | 9 |
| 6 | 39 |
| 7 | 197 |
| 8 | 721 |
| 9 | 2717 |
| 10 | 8211 |
| 11 | 19836 |
| 12 | 74497 |
| 13 | 132611 |
| 14 | 403534 |
| 15 | 1127416 |
| 16 | 2364402 |
| 17 | 4173316 |
| 18 | 15604400 |
| 19 | 21318428 |
| 20 | 73965916 |
| 21 | 154211880 |