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 | 1 |
| 3 | 18 |
| 4 | 216 |
| 5 | 2160 |
| 6 | 19440 |
| 7 | 163296 |
| 8 | 1306368 |
| 9 | 10077696 |
| 10 | 75582720 |
| 11 | 554273280 |
| 12 | 3990767616 |
| 13 | 28298170368 |
| 14 | 198087192576 |
| 15 | 1371372871680 |
| 16 | 9403699691520 |
| 17 | 63945157902336 |
| 18 | 431629815840768 |
| 19 | 2894458765049856 |
| 20 | 19296391766999040 |