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 | 2 |
| 2 | 7 |
| 3 | 31 |
| 4 | 165 |
| 5 | 1031 |
| 6 | 7423 |
| 7 | 60621 |
| 8 | 554249 |
| 9 | 5611771 |
| 10 | 62353011 |
| 11 | 754471433 |
| 12 | 9876716941 |
| 13 | 139097096919 |
| 14 | 2097156230471 |
| 15 | 33704296561141 |
| 16 | 575219994643473 |
| 17 | 10389911153247731 |
| 18 | 198019483156015579 |
| 19 | 3971390745517868001 |
| 20 | 83608226221428800021 |
| 21 | 1843561388182505040463 |