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 | 0 |
| 1 | 0 |
| 2 | 1 |
| 3 | 3 |
| 4 | 9 |
| 5 | 45 |
| 6 | 285 |
| 7 | 1995 |
| 8 | 15855 |
| 9 | 142695 |
| 10 | 1427895 |
| 11 | 15706845 |
| 12 | 188471745 |
| 13 | 2450132685 |
| 14 | 34301992725 |
| 15 | 514529890875 |
| 16 | 8232476226975 |
| 17 | 139952095858575 |
| 18 | 2519137759913775 |
| 19 | 47863617438361725 |
| 20 | 957272348112505425 |
| 21 | 20102719310362613925 |
| 22 | 442259824841726816925 |
| 23 | 10171975971359716789275 |