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%I #5 Oct 10 2019 00:34:26
%S 0,0,0,5,409,7,2621,971,1677721,1342177,107,89,6871947673,54975581,
%T 4398046511,883,28147497671,2251799813,180143985094819,1518807585587,
%U 46068469,3685477,629483,9029581035870565171,472236648286964521369
%N Largest prime substring in 8^n (0 if none).
%Y Cf. A046266.
%K nonn
%O 0,4
%A _Patrick De Geest_, Jun 15 1998