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 | 0 |
| 2 | 0 |
| 3 | 0 |
| 4 | 1 |
| 5 | 4 |
| 6 | 16 |
| 7 | 64 |
| 8 | 236 |
| 9 | 818 |
| 10 | 2736 |
| 11 | 8934 |
| 12 | 28622 |
| 13 | 90324 |
| 14 | 281792 |
| 15 | 871556 |
| 16 | 2677750 |
| 17 | 8184383 |
| 18 | 24913238 |
| 19 | 75593383 |
| 20 | 228793147 |
| 21 | 691094857 |
| 22 | 2084237036 |
| 23 | 6277871658 |
| 24 | 18890568921 |
| 25 | 56798001639 |
| 26 | 170665733660 |
| 27 | 512554832309 |
| 28 | 1538718547049 |