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A187823 as a simple table

na(n)
15
217
373
4257
5757
665537
7262657
81772893
94432676798593
1048551233240513
11378890487846991
123156404483062657
1317390284913300671
14280343912759041771
15319913861581383373
16487014306953858713
175559917315850179173
187824668707707203971
198443914727229480773
2032564717507686012813

[5,17,73,257,757,65537,262657,1772893,
 4432676798593,48551233240513,378890487846991,
 3156404483062657,17390284913300671,
 280343912759041771,319913861581383373,
 487014306953858713,5559917315850179173,
 7824668707707203971,8443914727229480773,
 32564717507686012813]