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 | 1 |
| 2 | 7 |
| 3 | 63 |
| 4 | 504 |
| 5 | 4095 |
| 6 | 32697 |
| 7 | 262143 |
| 8 | 2096640 |
| 9 | 16777152 |
| 10 | 134213625 |
| 11 | 1073741823 |
| 12 | 8589901320 |
| 13 | 68719476735 |
| 14 | 549755551737 |
| 15 | 4398046506945 |
| 16 | 35184369991680 |
| 17 | 281474976710655 |
| 18 | 2251799796875328 |
| 19 | 18014398509481983 |
| 20 | 144115187941637640 |
| 21 | 1152921504606584769 |