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 | 1 |
| 1 | 15 |
| 2 | 127 |
| 3 | 1023 |
| 4 | 8191 |
| 5 | 65535 |
| 6 | 524287 |
| 7 | 4194303 |
| 8 | 33554431 |
| 9 | 268435455 |
| 10 | 2147483647 |
| 11 | 17179869183 |
| 12 | 137438953471 |
| 13 | 1099511627775 |
| 14 | 8796093022207 |
| 15 | 70368744177663 |
| 16 | 562949953421311 |
| 17 | 4503599627370495 |
| 18 | 36028797018963967 |
| 19 | 288230376151711743 |
| 20 | 2305843009213693951 |
| 21 | 18446744073709551615 |