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 | 1 |
| 3 | 3 |
| 4 | 15 |
| 5 | 95 |
| 6 | 735 |
| 7 | 6727 |
| 8 | 71169 |
| 9 | 854919 |
| 10 | 11497845 |
| 11 | 171179261 |
| 12 | 2795081751 |
| 13 | 49668211177 |
| 14 | 954226247247 |
| 15 | 19709181213555 |
| 16 | 435524370171393 |
| 17 | 10252531220906051 |
| 18 | 256148413939459917 |
| 19 | 6769302493147288885 |
| 20 | 188664988853982963735 |
| 21 | 5530544750788380455433 |