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A290621 as a simple table

na(n)
01
11
27
315
47
563
663
7255
8511
91023
10127
114095
12255
1316383
142047
1565535
1612799
17262143
18102399
191048575
201015807
214194303
228388607
2316777215
2416515071
2567108863
2633357823
27268435455
287995391
291073741823
304194303
314294967295
3216252927
3317179869183

[1,1,7,15,7,63,63,255,511,1023,127,4095,255,16383,
 2047,65535,12799,262143,102399,1048575,1015807,
 4194303,8388607,16777215,16515071,67108863,
 33357823,268435455,7995391,1073741823,4194303,
 4294967295,16252927,17179869183]