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 | 2 |
| 3 | 6 |
| 4 | 46 |
| 5 | 340 |
| 6 | 3308 |
| 7 | 36288 |
| 8 | 460752 |
| 9 | 6551424 |
| 10 | 103685232 |
| 11 | 1803956880 |
| 12 | 34247483664 |
| 13 | 704301934752 |
| 14 | 15598712592864 |
| 15 | 370149922235520 |
| 16 | 9369093828260736 |
| 17 | 251968378971718656 |
| 18 | 7174943434198029312 |