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 | 7 |
| 2 | 63 |
| 3 | 511 |
| 4 | 4095 |
| 5 | 32767 |
| 6 | 262143 |
| 7 | 2097151 |
| 8 | 16777215 |
| 9 | 134217727 |
| 10 | 1073741823 |
| 11 | 8589934591 |
| 12 | 68719476735 |
| 13 | 549755813887 |
| 14 | 4398046511103 |
| 15 | 35184372088831 |
| 16 | 281474976710655 |
| 17 | 2251799813685247 |
| 18 | 18014398509481983 |