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 | 1 |
| 1 | 7 |
| 2 | 60 |
| 3 | 503 |
| 4 | 4080 |
| 5 | 32743 |
| 6 | 262108 |
| 7 | 2097103 |
| 8 | 16777152 |
| 9 | 134217647 |
| 10 | 1073741724 |
| 11 | 8589934471 |
| 12 | 68719476592 |
| 13 | 549755813719 |
| 14 | 4398046510908 |
| 15 | 35184372088607 |
| 16 | 281474976710400 |
| 17 | 2251799813684959 |
| 18 | 18014398509481660 |