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 | 0 |
| 1 | 1 |
| 2 | 0 |
| 3 | 3 |
| 4 | 8 |
| 5 | 25 |
| 6 | 72 |
| 7 | 203 |
| 8 | 560 |
| 9 | 1521 |
| 10 | 4080 |
| 11 | 10835 |
| 12 | 28536 |
| 13 | 74633 |
| 14 | 194040 |
| 15 | 501915 |
| 16 | 1292512 |
| 17 | 3315425 |
| 18 | 8474976 |
| 19 | 21597091 |
| 20 | 54884200 |
| 21 | 139127289 |
| 22 | 351877416 |
| 23 | 888121195 |
| 24 | 2237336592 |
| 25 | 5626467025 |
| 26 | 14126832720 |
| 27 | 35416929267 |
| 28 | 88670846936 |