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 | 0 |
| 2 | 1 |
| 3 | 3 |
| 4 | 15 |
| 5 | 87 |
| 6 | 687 |
| 7 | 6447 |
| 8 | 71967 |
| 9 | 918687 |
| 10 | 13256607 |
| 11 | 212840607 |
| 12 | 3765435807 |
| 13 | 72741666207 |
| 14 | 1523637512607 |
| 15 | 34389853295007 |
| 16 | 832071217775007 |
| 17 | 21482864837231007 |
| 18 | 589515687506543007 |
| 19 | 17133249343107695007 |
| 20 | 525731414152434287007 |
| 21 | 16984313499467403887007 |