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 | 20 |
| 5 | 72 |
| 6 | 290 |
| 7 | 1198 |
| 8 | 5452 |
| 9 | 25176 |
| 10 | 125874 |
| 11 | 637926 |
| 12 | 3448708 |
| 13 | 18919048 |
| 14 | 109412210 |
| 15 | 642798510 |
| 16 | 3945170012 |
| 17 | 24614491704 |
| 18 | 159328958690 |
| 19 | 1048645656646 |
| 20 | 7122719571700 |
| 21 | 49185991168968 |
| 22 | 349097516604738 |
| 23 | 2518145666958126 |
| 24 | 18609525157571692 |
| 25 | 139704193446510616 |