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 | 0 |
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 5 |
| 5 | 19 |
| 6 | 90 |
| 7 | 520 |
| 8 | 3475 |
| 9 | 26550 |
| 10 | 228050 |
| 11 | 2177020 |
| 12 | 22860090 |
| 13 | 261870070 |
| 14 | 3249793360 |
| 15 | 43432062300 |
| 16 | 621911561150 |
| 17 | 9498946124800 |
| 18 | 154152712434600 |
| 19 | 2648808048264400 |
| 20 | 48043086765929200 |
| 21 | 917249983543337400 |