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 | 0 |
| 4 | 12 |
| 5 | 50 |
| 6 | 405 |
| 7 | 3234 |
| 8 | 29680 |
| 9 | 300348 |
| 10 | 3337425 |
| 11 | 40382540 |
| 12 | 528644556 |
| 13 | 7445076990 |
| 14 | 112248853717 |
| 15 | 1803999433950 |
| 16 | 30788257007040 |
| 17 | 556112892188504 |
| 18 | 10598857474652865 |
| 19 | 212565974908314168 |
| 20 | 4475073155964510700 |