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 | 3 |
| 2 | 20 |
| 3 | 189 |
| 4 | 2232 |
| 5 | 31130 |
| 6 | 497016 |
| 7 | 8907885 |
| 8 | 176829104 |
| 9 | 3849436062 |
| 10 | 91187523000 |
| 11 | 2335691914050 |
| 12 | 64344487654800 |
| 13 | 1897619527612692 |
| 14 | 59667237154623280 |
| 15 | 1993022006345620605 |
| 16 | 70488571028815935072 |
| 17 | 2631925423768158446390 |
| 18 | 103469607286411235941944 |
| 19 | 4272438866376100717458486 |