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A131898 as a simple table

na(n)
01
15
211
321
439
573
6139
7269
8527
91041
102067
114117
128215
1316409
1432795
1565565
16131103
17262177
18524323
191048613
202097191
214194345
228388651
2316777261
2433554479
2567108913
26134217779
27268435509
28536870967
291073741881
302147483707
314294967357
328589934655
3317179869249

[1,5,11,21,39,73,139,269,527,1041,2067,4117,8215,
 16409,32795,65565,131103,262177,524323,1048613,
 2097191,4194345,8388651,16777261,33554479,
 67108913,134217779,268435509,536870967,1073741881,
 2147483707,4294967357,8589934655,17179869249]