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 | 1 |
| 2 | 4 |
| 3 | 48 |
| 4 | 320 |
| 5 | 2816 |
| 6 | 21504 |
| 7 | 176128 |
| 8 | 1392640 |
| 9 | 11206656 |
| 10 | 89391104 |
| 11 | 716177408 |
| 12 | 5725224960 |
| 13 | 45818576896 |
| 14 | 366481506304 |
| 15 | 2932120485888 |
| 16 | 23455890145280 |
| 17 | 187651416129536 |
| 18 | 1501194149167104 |
| 19 | 12009621912813568 |
| 20 | 96076700424601600 |