OFFSET
1,1
COMMENTS
Or numbers n such that the smallest prime divisor of n^2+1 is A002313(4).
a(n)== 4 or 30 (mod 34).
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
EXAMPLE
30 is in the sequence because 30^2+1= 17*53.
MATHEMATICA
lst={}; Do[If[FactorInteger[n^2+1][[1, 1]]==17, AppendTo[lst, n]], {n, 2, 2000}]; lst
p = 17; ps = Select[Range[p - 1], Mod[#, 4] != 3 && PrimeQ[#] &]; Select[Range[1670], Divisible[(nn = #^2 + 1), p] && ! Or @@ Divisible[nn, ps] &] (* Amiram Eldar, Aug 16 2019 *)
PROG
(Magma) [n: n in [2..2000] | PrimeDivisors(n^2+1)[1] eq 17]; // Bruno Berselli, Oct 08 2014
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Michel Lagneau, Oct 08 2014
STATUS
approved