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 | 1 |
| 2 | 0 |
| 3 | 0 |
| 4 | 2 |
| 5 | 10 |
| 6 | 0 |
| 7 | 8 |
| 8 | 24 |
| 9 | 72 |
| 10 | 116 |
| 11 | 336 |
| 12 | 1124 |
| 13 | 4056 |
| 14 | 12628 |
| 15 | 58984 |
| 16 | 263066 |
| 17 | 1124116 |
| 18 | 5388972 |
| 19 | 29219680 |
| 20 | 173696136 |
| 21 | 967249940 |