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 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 30 |
| 5 | 114 |
| 6 | 402 |
| 7 | 1386 |
| 8 | 4746 |
| 9 | 16218 |
| 10 | 55386 |
| 11 | 189114 |
| 12 | 645690 |
| 13 | 2204538 |
| 14 | 7526778 |
| 15 | 25698042 |
| 16 | 87738618 |
| 17 | 299558394 |
| 18 | 1022756346 |
| 19 | 3491908602 |
| 20 | 11922121722 |
| 21 | 40704669690 |
| 22 | 138974435322 |
| 23 | 474488401914 |
| 24 | 1620004737018 |
| 25 | 5531042144250 |
| 26 | 18884159102970 |
| 27 | 64474552123386 |