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 | 0 |
| 2 | 1 |
| 3 | 7 |
| 4 | 31 |
| 5 | 511 |
| 6 | 2047 |
| 7 | 32767 |
| 8 | 131071 |
| 9 | 2097151 |
| 10 | 134217727 |
| 11 | 536870911 |
| 12 | 34359738367 |
| 13 | 549755813887 |
| 14 | 2199023255551 |
| 15 | 35184372088831 |
| 16 | 2251799813685247 |
| 17 | 144115188075855871 |
| 18 | 576460752303423487 |
| 19 | 36893488147419103231 |
| 20 | 590295810358705651711 |