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 | 6 |
| 2 | 24 |
| 3 | 90 |
| 4 | 336 |
| 5 | 1254 |
| 6 | 4680 |
| 7 | 17466 |
| 8 | 65184 |
| 9 | 243270 |
| 10 | 907896 |
| 11 | 3388314 |
| 12 | 12645360 |
| 13 | 47193126 |
| 14 | 176127144 |
| 15 | 657315450 |
| 16 | 2453134656 |
| 17 | 9155223174 |
| 18 | 34167758040 |
| 19 | 127515808986 |
| 20 | 475895477904 |
| 21 | 1776066102630 |
| 22 | 6628368932616 |
| 23 | 24737409627834 |
| 24 | 92321269578720 |
| 25 | 344547668687046 |