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 | 2 |
| 3 | 12 |
| 4 | 126 |
| 5 | 252 |
| 6 | 504 |
| 7 | 2040 |
| 8 | 4080 |
| 9 | 16380 |
| 10 | 32760 |
| 11 | 65520 |
| 12 | 524286 |
| 13 | 1048572 |
| 14 | 4194300 |
| 15 | 8388600 |
| 16 | 134217720 |
| 17 | 268435440 |
| 18 | 7516192740 |
| 19 | 10737418230 |
| 20 | 21474836460 |
| 21 | 137438953440 |
| 22 | 274877906880 |
| 23 | 274877906940 |
| 24 | 549755813880 |
| 25 | 8796093022200 |
| 26 | 8796093022206 |
| 27 | 17592186044412 |