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 | 1 |
| 3 | 3 |
| 4 | 20 |
| 5 | 160 |
| 6 | 1727 |
| 7 | 22341 |
| 8 | 337947 |
| 9 | 5799881 |
| 10 | 111180832 |
| 11 | 2352448424 |
| 12 | 54449597409 |
| 13 | 1368516031855 |
| 14 | 37118127188225 |
| 15 | 1080644471447419 |
| 16 | 33614180067524196 |
| 17 | 1112586937337720904 |
| 18 | 39043623554061199807 |
| 19 | 1448021297870473796645 |
| 20 | 56592256120004219495755 |
| 21 | 2324706946641972649074513 |