| n | a(n) |
|---|---|
| 0 | 0 |
| 1 | 1 |
| 2 | 1 |
| 3 | 3 |
| 4 | 7 |
| 5 | 31 |
| 6 | 255 |
| 7 | 8191 |
| 8 | 2097151 |
| 9 | 17179869183 |
| 10 | 36028797018963967 |
| 11 | 618970019642690137449562111 |
| 12 | 22300745198530623141535718272648361505980415 |
[0,1,1,3,7,31,255,8191,2097151,17179869183, 36028797018963967,618970019642690137449562111, 22300745198530623141535718272648361505980415] |