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 | 2 |
| 3 | 12 |
| 4 | 80 |
| 5 | 630 |
| 6 | 5816 |
| 7 | 61978 |
| 8 | 751222 |
| 9 | 10225140 |
| 10 | 154610048 |
| 11 | 2573280820 |
| 12 | 46775427860 |
| 13 | 922374085984 |
| 14 | 19616567407368 |
| 15 | 447666534959528 |
| 16 | 10913339500879576 |
| 17 | 283081184691349600 |
| 18 | 7785415448640271232 |
| 19 | 226306589802176060640 |
| 20 | 6933002797216545295968 |