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) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 4 |
| 4 | 18 |
| 5 | 144 |
| 6 | 1200 |
| 7 | 14400 |
| 8 | 176400 |
| 9 | 2822400 |
| 10 | 45722880 |
| 11 | 914457600 |
| 12 | 18441561600 |
| 13 | 442597478400 |
| 14 | 10685567692800 |
| 15 | 299195895398400 |
| 16 | 8414884558080000 |
| 17 | 269276305858560000 |
| 18 | 8646761377013760000 |
| 19 | 311283409572495360000 |