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 | 3 |
| 4 | 15 |
| 5 | 75 |
| 6 | 435 |
| 7 | 3045 |
| 8 | 24465 |
| 9 | 220185 |
| 10 | 2200905 |
| 11 | 24209955 |
| 12 | 290529855 |
| 13 | 3776888115 |
| 14 | 52876298475 |
| 15 | 793144477125 |
| 16 | 12690313661025 |
| 17 | 215735332237425 |
| 18 | 3883235945814225 |
| 19 | 73781482970470275 |
| 20 | 1475629660064134575 |
| 21 | 30988222861346826075 |
| 22 | 681740902935880863075 |