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 | 1 |
| 3 | 0 |
| 4 | 1 |
| 5 | 2 |
| 6 | 7 |
| 7 | 27 |
| 8 | 126 |
| 9 | 664 |
| 10 | 3954 |
| 11 | 26190 |
| 12 | 190754 |
| 13 | 1514332 |
| 14 | 12998035 |
| 15 | 119803771 |
| 16 | 1178740932 |
| 17 | 12316480222 |
| 18 | 136060611189 |
| 19 | 1582930919092 |
| 20 | 19328253734491 |