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 | 12 |
| 5 | 20 |
| 6 | 1470 |
| 7 | 12642 |
| 8 | 70616 |
| 9 | 2131992 |
| 10 | 39352410 |
| 11 | 470186750 |
| 12 | 11032124532 |
| 13 | 295053244356 |
| 14 | 5896487364950 |
| 15 | 146264289411450 |
| 16 | 4625791393554480 |
| 17 | 130492119237611312 |
| 18 | 3837833086814864946 |
| 19 | 135471306780659593206 |
| 20 | 4800394977109827314060 |