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 | 1 |
| 1 | 3 |
| 2 | 12 |
| 3 | 30 |
| 4 | 90 |
| 5 | 210 |
| 6 | 560 |
| 7 | 1260 |
| 8 | 3150 |
| 9 | 6930 |
| 10 | 16632 |
| 11 | 36036 |
| 12 | 84084 |
| 13 | 180180 |
| 14 | 411840 |
| 15 | 875160 |
| 16 | 1969110 |
| 17 | 4157010 |
| 18 | 9237800 |
| 19 | 19399380 |
| 20 | 42678636 |
| 21 | 89237148 |
| 22 | 194699232 |
| 23 | 405623400 |
| 24 | 878850700 |
| 25 | 1825305300 |
| 26 | 3931426800 |
| 27 | 8143669800 |
| 28 | 17450721000 |