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 | 0 |
| 4 | 18 |
| 5 | 30 |
| 6 | 510 |
| 7 | 1470 |
| 8 | 22890 |
| 9 | 284550 |
| 10 | 3171630 |
| 11 | 18486930 |
| 12 | 45347610 |
| 13 | 4254260010 |
| 14 | 2349577230 |
| 15 | 371965003410 |
| 16 | 9252750236730 |
| 17 | 190224835871070 |
| 18 | 221717289063270 |
| 19 | 14855058367239090 |
| 20 | 1662934646118135390 |
| 21 | 45974266913148043470 |
| 22 | 4510191947325194130 |