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) |
|---|---|
| 1 | 4 |
| 2 | 6 |
| 3 | 16 |
| 4 | 45 |
| 5 | 132 |
| 6 | 404 |
| 7 | 1296 |
| 8 | 4380 |
| 9 | 15064 |
| 10 | 53622 |
| 11 | 192696 |
| 12 | 703895 |
| 13 | 2589300 |
| 14 | 9606744 |
| 15 | 35824088 |
| 16 | 134297280 |
| 17 | 505421340 |
| 18 | 1909194056 |
| 19 | 7234153416 |
| 20 | 27489073899 |
| 21 | 104717489748 |
| 22 | 399827555604 |
| 23 | 1529763696816 |