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) |
|---|---|
| 3 | 0 |
| 4 | 2 |
| 5 | 6 |
| 6 | 20 |
| 7 | 66 |
| 8 | 210 |
| 9 | 652 |
| 10 | 1988 |
| 11 | 5982 |
| 12 | 17830 |
| 13 | 52782 |
| 14 | 155480 |
| 15 | 456364 |
| 16 | 1336066 |
| 17 | 3904280 |
| 18 | 11394244 |
| 19 | 33222902 |
| 20 | 96812174 |
| 21 | 282009512 |
| 22 | 821327088 |
| 23 | 2391918708 |
| 24 | 6966267782 |
| 25 | 20291422370 |
| 26 | 59116724728 |
| 27 | 172271893036 |
| 28 | 502157965938 |