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 | 3 |
| 3 | 20 |
| 4 | 210 |
| 5 | 3003 |
| 6 | 54264 |
| 7 | 1184040 |
| 8 | 30260340 |
| 9 | 886163135 |
| 10 | 29248649430 |
| 11 | 1074082795968 |
| 12 | 43430966148115 |
| 13 | 1917283000904460 |
| 14 | 91748617512913200 |
| 15 | 4730523156632595024 |
| 16 | 261429178502421685800 |
| 17 | 15415916972482007401455 |
| 18 | 966121413245991846673830 |
| 19 | 64123483527473864490450300 |