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) |
|---|---|
| 2 | 4 |
| 3 | 18 |
| 4 | 72 |
| 5 | 270 |
| 6 | 972 |
| 7 | 3402 |
| 8 | 11664 |
| 9 | 39366 |
| 10 | 131220 |
| 11 | 433026 |
| 12 | 1417176 |
| 13 | 4605822 |
| 14 | 14880348 |
| 15 | 47829690 |
| 16 | 153055008 |
| 17 | 487862838 |
| 18 | 1549681956 |
| 19 | 4907326194 |
| 20 | 15496819560 |
| 21 | 48814981614 |
| 22 | 153418513644 |
| 23 | 481176247338 |
| 24 | 1506290861232 |
| 25 | 4707158941350 |