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 | 3 |
| 1 | 6 |
| 2 | 18 |
| 3 | 84 |
| 4 | 258 |
| 5 | 1302 |
| 6 | 4356 |
| 7 | 20520 |
| 8 | 65538 |
| 9 | 351120 |
| 10 | 1110276 |
| 11 | 5048232 |
| 12 | 17041416 |
| 13 | 82623888 |
| 14 | 284225796 |
| 15 | 1494039792 |
| 16 | 4301668356 |
| 17 | 20788904016 |
| 18 | 73234343952 |
| 19 | 332019460560 |
| 20 | 1103789883396 |
| 21 | 5936210280000 |
| 22 | 18679788287496 |
| 23 | 84884999116320 |
| 24 | 282937726148616 |