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) |
|---|---|
| 2 | 0 |
| 3 | 2 |
| 4 | 10 |
| 5 | 42 |
| 6 | 168 |
| 7 | 660 |
| 8 | 2574 |
| 9 | 10010 |
| 10 | 38896 |
| 11 | 151164 |
| 12 | 587860 |
| 13 | 2288132 |
| 14 | 8914800 |
| 15 | 34767720 |
| 16 | 135727830 |
| 17 | 530365050 |
| 18 | 2074316640 |
| 19 | 8119857900 |
| 20 | 31810737420 |
| 21 | 124718287980 |
| 22 | 489325340400 |
| 23 | 1921133836440 |
| 24 | 7547311500300 |
| 25 | 29667795388452 |
| 26 | 116686713634848 |