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 | 2 |
| 3 | 6 |
| 4 | 30 |
| 5 | 42 |
| 6 | 66 |
| 7 | 2730 |
| 8 | 14322 |
| 9 | 1919190 |
| 10 | 56786730 |
| 11 | 140100870 |
| 12 | 209191710 |
| 13 | 2328255930 |
| 14 | 2381714790 |
| 15 | 7225713885390 |
| 16 | 9538864545210 |
| 17 | 21626561658972270 |
| 18 | 446617991732222310 |
| 19 | 115471236091149548610 |
| 20 | 5145485882746933233510 |
| 21 | 14493038256293268734790 |