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 | 6 |
| 4 | 18 |
| 5 | 75 |
| 6 | 295 |
| 7 | 1575 |
| 8 | 7196 |
| 9 | 48993 |
| 10 | 230413 |
| 11 | 2164767 |
| 12 | 8055938 |
| 13 | 139431149 |
| 14 | 70125991 |
| 15 | 14201296057 |
| 16 | -77573062280 |
| 17 | 2389977322593 |
| 18 | -28817693086263 |
| 19 | 615493949444827 |
| 20 | -10403976760589602 |
| 21 | 215611836994976237 |