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 | 6 |
| 3 | 30 |
| 4 | 152 |
| 5 | 840 |
| 6 | 5232 |
| 7 | 37072 |
| 8 | 297600 |
| 9 | 2680704 |
| 10 | 26812160 |
| 11 | 294945024 |
| 12 | 3539364864 |
| 13 | 46011796480 |
| 14 | 644165265408 |
| 15 | 9662479226880 |
| 16 | 154599668154368 |
| 17 | 2628194359738368 |
| 18 | 47307498477649920 |
| 19 | 898842471080329216 |