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 | 0 |
| 3 | 1 |
| 4 | 4 |
| 5 | 23 |
| 6 | 110 |
| 7 | 719 |
| 8 | 4992 |
| 9 | 40302 |
| 10 | 362492 |
| 11 | 3628799 |
| 12 | 39912804 |
| 13 | 479001599 |
| 14 | 6226974714 |
| 15 | 87178289207 |
| 16 | 1307673722880 |
| 17 | 20922789887999 |
| 18 | 355687417744992 |
| 19 | 6402373705727999 |
| 20 | 121645100223036700 |
| 21 | 2432902008176115023 |
| 22 | 51090942167993548790 |
| 23 | 1124000727777607679999 |