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 | 2 |
| 4 | 7 |
| 5 | 23 |
| 6 | 122 |
| 7 | 888 |
| 8 | 11302 |
| 9 | 262322 |
| 10 | 11730500 |
| 11 | 1006992696 |
| 12 | 164072174728 |
| 13 | 50336940195360 |
| 14 | 29003653625867536 |
| 15 | 31397431814147073280 |
| 16 | 63969589218557753586160 |
| 17 | 245871863137828405125824848 |
| 18 | 1787331789281458167615194471072 |
| 19 | 24636021675399858912682459613241920 |