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 | 1 |
| 2 | 2 |
| 3 | 4 |
| 4 | 12 |
| 5 | 52 |
| 6 | 288 |
| 7 | 1912 |
| 8 | 14720 |
| 9 | 128656 |
| 10 | 1257120 |
| 11 | 13571008 |
| 12 | 160337856 |
| 13 | 2057250112 |
| 14 | 28480825856 |
| 15 | 423097887616 |
| 16 | 6712604550144 |
| 17 | 113268081577216 |
| 18 | 2025400259289600 |
| 19 | 38256068763347968 |
| 20 | 761070574748380160 |