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 | 1 |
| 2 | 2 |
| 3 | 0 |
| 4 | 0 |
| 5 | 2 |
| 6 | 4 |
| 7 | 10 |
| 8 | 36 |
| 9 | 126 |
| 10 | 454 |
| 11 | 1744 |
| 12 | 6892 |
| 13 | 28486 |
| 14 | 120962 |
| 15 | 531660 |
| 16 | 2398248 |
| 17 | 11127674 |
| 18 | 52888998 |
| 19 | 257570104 |
| 20 | 1282439216 |