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) |
|---|---|
| 2 | 6 |
| 3 | 15 |
| 4 | 42 |
| 5 | 132 |
| 6 | 456 |
| 7 | 1680 |
| 8 | 6432 |
| 9 | 25152 |
| 10 | 99456 |
| 11 | 395520 |
| 12 | 1577472 |
| 13 | 6300672 |
| 14 | 25184256 |
| 15 | 100700160 |
| 16 | 402726912 |
| 17 | 1610760192 |
| 18 | 6442745856 |
| 19 | 25770393600 |
| 20 | 103080394752 |
| 21 | 412319219712 |
| 22 | 1649272160256 |
| 23 | 6597079203840 |
| 24 | 26388297940992 |
| 25 | 105553154015232 |
| 26 | 422212540563456 |
| 27 | 1688850011258880 |
| 28 | 6755399743045632 |