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 | 8 |
| 1 | 15 |
| 2 | 71 |
| 3 | 519 |
| 4 | 4103 |
| 5 | 32775 |
| 6 | 262151 |
| 7 | 2097159 |
| 8 | 16777223 |
| 9 | 134217735 |
| 10 | 1073741831 |
| 11 | 8589934599 |
| 12 | 68719476743 |
| 13 | 549755813895 |
| 14 | 4398046511111 |
| 15 | 35184372088839 |
| 16 | 281474976710663 |
| 17 | 2251799813685255 |
| 18 | 18014398509481991 |
| 19 | 144115188075855879 |
| 20 | 1152921504606846983 |