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 | 0 |
| 1 | 0 |
| 2 | 3 |
| 3 | 15 |
| 4 | 51 |
| 5 | 165 |
| 6 | 507 |
| 7 | 1551 |
| 8 | 4683 |
| 9 | 14127 |
| 10 | 42459 |
| 11 | 127599 |
| 12 | 383019 |
| 13 | 1149693 |
| 14 | 3449715 |
| 15 | 10351023 |
| 16 | 31054947 |
| 17 | 93170397 |
| 18 | 279516747 |
| 19 | 838566831 |
| 20 | 2515717083 |
| 21 | 7547200797 |
| 22 | 22641651939 |
| 23 | 67925104239 |
| 24 | 203775461139 |
| 25 | 611326828047 |
| 26 | 1833980928771 |