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A289940 as a simple table

na(n)
01
11
27
315
47
515
631
763
831
963
10127
11255
12511
131023
142047
154095
16511
171023
182047
194095
208191
2116383
2232767
2365535
24131071
25262143
26524287
271048575
282097151
294194303
308388607
3116777215
32131071
33262143
34524287
351048575
3652428799
37104857599
383430940671

[1,1,7,15,7,15,31,63,31,63,127,255,511,1023,2047,
 4095,511,1023,2047,4095,8191,16383,32767,65535,
 131071,262143,524287,1048575,2097151,4194303,
 8388607,16777215,131071,262143,524287,1048575,
 52428799,104857599,3430940671]