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 | 1 |
| 3 | 2 |
| 4 | 6 |
| 5 | 20 |
| 6 | 120 |
| 7 | 420 |
| 8 | 2688 |
| 9 | 18144 |
| 10 | 120960 |
| 11 | 1330560 |
| 12 | 7983360 |
| 13 | 103783680 |
| 14 | 1037836800 |
| 15 | 12454041600 |
| 16 | 149448499200 |
| 17 | 1693749657600 |
| 18 | 30487493836800 |
| 19 | 289631191449600 |
| 20 | 5792623828992000 |
| 21 | 121645100408832000 |
| 22 | 2676192208994304000 |
| 23 | 30776210403434496000 |