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) |
|---|---|
| 3 | 1 |
| 4 | 4 |
| 5 | 15 |
| 6 | 54 |
| 7 | 189 |
| 8 | 648 |
| 9 | 2187 |
| 10 | 7290 |
| 11 | 24057 |
| 12 | 78732 |
| 13 | 255879 |
| 14 | 826686 |
| 15 | 2657205 |
| 16 | 8503056 |
| 17 | 27103491 |
| 18 | 86093442 |
| 19 | 272629233 |
| 20 | 860934420 |
| 21 | 2711943423 |
| 22 | 8523250758 |
| 23 | 26732013741 |
| 24 | 83682825624 |
| 25 | 261508830075 |
| 26 | 815907549834 |
| 27 | 2541865828329 |