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 | 3 |
| 2 | 7 |
| 3 | 31 |
| 4 | 127 |
| 5 | 2047 |
| 6 | 8191 |
| 7 | 131071 |
| 8 | 524287 |
| 9 | 8388607 |
| 10 | 536870911 |
| 11 | 2147483647 |
| 12 | 137438953471 |
| 13 | 2199023255551 |
| 14 | 8796093022207 |
| 15 | 140737488355327 |
| 16 | 9007199254740991 |
| 17 | 576460752303423487 |
| 18 | 2305843009213693951 |
| 19 | 147573952589676412927 |
| 20 | 2361183241434822606847 |