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 | 3 |
| 2 | 15 |
| 3 | 120 |
| 4 | 528 |
| 5 | 4095 |
| 6 | 139128 |
| 7 | 160554240 |
| 8 | 812293020528 |
| 9 | 379188080252621270252095320 |