[Maple], 106 [bytes]
For n = 7 returns {2, 3, 7, 13, 43, 139, 547} in 0.5 seconds.
a:=proc(n)p:=1;w:={};for k to n do p:=p^2+p;{seq(x[1],x=ifactors(p)[2])}minus w;w:=w union{min(%)}od end:
Sophia Antipolis
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