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 | 15 |
| 4 | 63 |
| 5 | 255 |
| 6 | 511 |
| 7 | 1023 |
| 8 | 2047 |
| 9 | 4095 |
| 10 | 16383 |
| 11 | 32767 |
| 12 | 65535 |
| 13 | 262143 |
| 14 | 1048575 |
| 15 | 2097151 |
| 16 | 4194303 |
| 17 | 8388607 |
| 18 | 16777215 |
| 19 | 33554431 |
| 20 | 67108863 |
| 21 | 134217727 |
| 22 | 268435455 |
| 23 | 536870911 |
| 24 | 1073741823 |
| 25 | 4294967295 |
| 26 | 8589934591 |
| 27 | 17179869183 |
| 28 | 34359738367 |