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 | 1 |
| 2 | 1 |
| 3 | 6 |
| 4 | 24 |
| 5 | 152 |
| 6 | 1230 |
| 7 | 12646 |
| 8 | 141274 |
| 9 | 1730984 |
| 10 | 23920800 |
| 11 | 379364664 |
| 12 | 6766026168 |
| 13 | 131337466608 |
| 14 | 2713274041296 |
| 15 | 59397879195456 |
| 16 | 1386647548658496 |
| 17 | 34745321580075648 |
| 18 | 934708252265232768 |
| 19 | 26835517455387452928 |
| 20 | 815158892950448937984 |