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 | 1 |
| 2 | 4 |
| 3 | 12 |
| 4 | 40 |
| 5 | 140 |
| 6 | 816 |
| 7 | 5082 |
| 8 | 40800 |
| 9 | 363258 |
| 10 | 3632880 |
| 11 | 39916910 |
| 12 | 479052528 |
| 13 | 6227020956 |
| 14 | 87178936992 |
| 15 | 1307674429440 |
| 16 | 20922800222848 |
| 17 | 355687428096272 |
| 18 | 6402373892575992 |
| 19 | 121645100408832342 |
| 20 | 2432902011892837920 |