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 | 8 |
| 5 | 56 |
| 6 | 640 |
| 7 | 10960 |
| 8 | 264640 |
| 9 | 8581760 |
| 10 | 360331520 |
| 11 | 19031302400 |
| 12 | 1235451750400 |
| 13 | 96722377139200 |
| 14 | 8988790940876800 |
| 15 | 978442125179648000 |
| 16 | 123324448870740377600 |
| 17 | 17820979140159760793600 |
| 18 | 2926936219425738642227200 |
| 19 | 542215853077506417192140800 |
| 20 | 112527512540808439576566169600 |