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) |
|---|---|
| 1 | 0 |
| 2 | 1 |
| 3 | 2 |
| 4 | 8 |
| 5 | 24 |
| 6 | 136 |
| 7 | 960 |
| 8 | 5312 |
| 9 | 40320 |
| 10 | 491776 |
| 11 | 4112640 |
| 12 | 40270592 |
| 13 | 638668800 |
| 14 | 6249389056 |
| 15 | 91883151360 |
| 16 | 1919826163712 |
| 17 | 20922789888000 |
| 18 | 355897293438976 |
| 19 | 8676514912665600 |
| 20 | 121674189293944832 |
| 21 | 2757288942600192000 |