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 | 0 |
| 2 | 1 |
| 3 | 3 |
| 4 | 6 |
| 5 | 10 |
| 6 | 30 |
| 7 | 126 |
| 8 | 448 |
| 9 | 1296 |
| 10 | 4140 |
| 11 | 17380 |
| 12 | 76296 |
| 13 | 296088 |
| 14 | 1126216 |
| 15 | 4940040 |
| 16 | 23904000 |
| 17 | 110455936 |
| 18 | 489602448 |
| 19 | 2313783216 |
| 20 | 11960299360 |
| 21 | 61878663840 |
| 22 | 309644323296 |
| 23 | 1587272962528 |
| 24 | 8699800221696 |
| 25 | 48793502304000 |
| 26 | 268603261201600 |
| 27 | 1487663739072576 |