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 | 1 |
| 2 | 0 |
| 3 | 0 |
| 4 | 0 |
| 5 | 2 |
| 6 | 4 |
| 7 | 18 |
| 8 | 48 |
| 9 | 156 |
| 10 | 472 |
| 11 | 1526 |
| 12 | 4852 |
| 13 | 16000 |
| 14 | 52940 |
| 15 | 178276 |
| 16 | 605520 |
| 17 | 2079862 |
| 18 | 7201084 |
| 19 | 25138878 |
| 20 | 88358520 |
| 21 | 312576996 |
| 22 | 1112087012 |
| 23 | 3977502766 |
| 24 | 14294093652 |
| 25 | 51596165872 |
| 26 | 186997738504 |
| 27 | 680272334202 |
| 28 | 2483340387644 |
| 29 | 9094756956908 |