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) |
|---|---|
| 1 | 1 |
| 2 | 1 |
| 3 | 2 |
| 4 | 4 |
| 5 | 10 |
| 6 | 24 |
| 7 | 70 |
| 8 | 192 |
| 9 | 576 |
| 10 | 1890 |
| 11 | 6300 |
| 12 | 21600 |
| 13 | 78848 |
| 14 | 294840 |
| 15 | 1143072 |
| 16 | 4572288 |
| 17 | 18849600 |
| 18 | 79968000 |
| 19 | 348566400 |
| 20 | 1559376000 |
| 21 | 7147140000 |
| 22 | 33522128640 |
| 23 | 160758097500 |
| 24 | 787652812800 |
| 25 | 3938264064000 |
| 26 | 20080974513600 |
| 27 | 104348440350000 |
| 28 | 552160113120000 |