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 | 0 |
| 2 | 0 |
| 3 | 2 |
| 4 | 8 |
| 5 | 41 |
| 6 | 231 |
| 7 | 1527 |
| 8 | 11610 |
| 9 | 99850 |
| 10 | 958561 |
| 11 | 10160755 |
| 12 | 117864768 |
| 13 | 1485096081 |
| 14 | 20197306708 |
| 15 | 294880677941 |
| 16 | 4600138575887 |
| 17 | 76362300359740 |
| 18 | 1343976486331425 |
| 19 | 24997962645764522 |
| 20 | 489960067856984638 |