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 | -3 |
| 1 | 0 |
| 2 | 12 |
| 3 | 60 |
| 4 | 252 |
| 5 | 1020 |
| 6 | 4092 |
| 7 | 16380 |
| 8 | 65532 |
| 9 | 262140 |
| 10 | 1048572 |
| 11 | 4194300 |
| 12 | 16777212 |
| 13 | 67108860 |
| 14 | 268435452 |
| 15 | 1073741820 |
| 16 | 4294967292 |
| 17 | 17179869180 |
| 18 | 68719476732 |
| 19 | 274877906940 |
| 20 | 1099511627772 |
| 21 | 4398046511100 |
| 22 | 17592186044412 |
| 23 | 70368744177660 |
| 24 | 281474976710652 |
| 25 | 1125899906842620 |