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 | 1 |
| 2 | 4 |
| 3 | 18 |
| 4 | 120 |
| 5 | 960 |
| 6 | 9360 |
| 7 | 105840 |
| 8 | 1370880 |
| 9 | 19958400 |
| 10 | 322963200 |
| 11 | 5748019200 |
| 12 | 111607372800 |
| 13 | 2347586841600 |
| 14 | 53178757632000 |
| 15 | 1290674601216000 |
| 16 | 33413695451136000 |
| 17 | 919096314200064000 |
| 18 | 26768324463648768000 |