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 | 2 |
| 3 | 6 |
| 4 | 26 |
| 5 | 143 |
| 6 | 880 |
| 7 | 6820 |
| 8 | 61270 |
| 9 | 612700 |
| 10 | 6740700 |
| 11 | 83088500 |
| 12 | 1211283600 |
| 13 | 17058212600 |
| 14 | 270017301300 |
| 15 | 4560302022000 |
| 16 | 82065335385000 |
| 17 | 1648341372414000 |
| 18 | 34076827548280000 |
| 19 | 725735500635080000 |
| 20 | 17178403115182870000 |