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 | 9 |
| 1 | 15 |
| 2 | 39 |
| 3 | 135 |
| 4 | 519 |
| 5 | 2055 |
| 6 | 8199 |
| 7 | 32775 |
| 8 | 131079 |
| 9 | 524295 |
| 10 | 2097159 |
| 11 | 8388615 |
| 12 | 33554439 |
| 13 | 134217735 |
| 14 | 536870919 |
| 15 | 2147483655 |
| 16 | 8589934599 |
| 17 | 34359738375 |
| 18 | 137438953479 |
| 19 | 549755813895 |
| 20 | 2199023255559 |
| 21 | 8796093022215 |
| 22 | 35184372088839 |
| 23 | 140737488355335 |
| 24 | 562949953421319 |
| 25 | 2251799813685255 |