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 | 9 |
| 2 | 21 |
| 3 | 69 |
| 4 | 201 |
| 5 | 609 |
| 6 | 1821 |
| 7 | 5469 |
| 8 | 16401 |
| 9 | 49209 |
| 10 | 147621 |
| 11 | 442869 |
| 12 | 1328601 |
| 13 | 3985809 |
| 14 | 11957421 |
| 15 | 35872269 |
| 16 | 107616801 |
| 17 | 322850409 |
| 18 | 968551221 |
| 19 | 2905653669 |
| 20 | 8716961001 |
| 21 | 26150883009 |
| 22 | 78452649021 |
| 23 | 235357947069 |
| 24 | 706073841201 |
| 25 | 2118221523609 |
| 26 | 6354664570821 |
| 27 | 19063993712469 |