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 | 0 |
| 3 | 0 |
| 4 | 18 |
| 5 | 90 |
| 6 | 690 |
| 7 | 4830 |
| 8 | 40110 |
| 9 | 362670 |
| 10 | 3628590 |
| 11 | 39914490 |
| 12 | 478999290 |
| 13 | 6226990770 |
| 14 | 87178261170 |
| 15 | 1307674337970 |
| 16 | 20922789857970 |
| 17 | 355687427585490 |
| 18 | 6402373705217490 |
| 19 | 121645100399132310 |
| 20 | 2432902008166940310 |