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 | 28 |
| 3 | 252 |
| 4 | 2600 |
| 5 | 29248 |
| 6 | 349132 |
| 7 | 4351944 |
| 8 | 56062681 |
| 9 | 741132648 |
| 10 | 10003860384 |
| 11 | 137367013012 |
| 12 | 1913480724898 |
| 13 | 26980497086268 |
| 14 | 384428067086544 |
| 15 | 5527398761722192 |