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 | 1 |
| 1 | 0 |
| 2 | 0 |
| 3 | 6 |
| 4 | 36 |
| 5 | 210 |
| 6 | 2070 |
| 7 | 24864 |
| 8 | 310632 |
| 9 | 4337544 |
| 10 | 68922360 |
| 11 | 1205002656 |
| 12 | 22844264256 |
| 13 | 469287123552 |
| 14 | 10397824478496 |
| 15 | 246800350393344 |
| 16 | 6246190572981120 |
| 17 | 167972669001740160 |
| 18 | 4783274802508890240 |
| 19 | 143775432034543203840 |
| 20 | 4548946867429143444480 |