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 | 3 |
| 1 | 1 |
| 2 | 3 |
| 3 | 15 |
| 4 | 95 |
| 5 | 690 |
| 6 | 5481 |
| 7 | 46376 |
| 8 | 411255 |
| 9 | 3781635 |
| 10 | 35791910 |
| 11 | 346821930 |
| 12 | 3427001253 |
| 13 | 34425730640 |
| 14 | 350732771160 |
| 15 | 3617153918640 |
| 16 | 37703805776935 |
| 17 | 396716804816265 |
| 18 | 4209161209968825 |
| 19 | 44993046668984145 |
| 20 | 484176486362971710 |