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%I #12 Aug 02 2021 12:25:55
%S 3121,78121,30517578121,710542735760100185871124267578121,
%T 413590306276513837435704346034981426782906055450439453121
%N Primes of the form 5^k - 4.
%e 3121 = 5^5 - 4 is prime and therefore is in the sequence.
%p n:=1000: S:={}: for i from 1 to n do if type(5^i-4,prime)=true then S:=S union {5^i-4} end if od; S;
%t Select[5^Range[90]-4,PrimeQ] (* _Harvey P. Dale_, Aug 23 2013 *)
%Y Cf. A059613, A135535, A228028.
%K nonn
%O 1,1
%A _Jonathan D. B. Hodgson_, Oct 12 2010
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