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A248549
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Numbers n such that the smallest prime divisor of n^2+1 is 61.
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5
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194, 316, 416, 804, 904, 926, 1026, 1170, 1270, 1414, 1536, 1780, 2024, 2490, 2734, 2856, 3000, 3100, 3244, 3344, 3366, 3610, 3954, 3976, 4320, 4564, 4830, 4930, 5074, 5196, 5540, 5684, 6394, 6416, 6516, 6760, 6904, 7004, 7126, 7270, 7370, 7514, 7614, 7736
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OFFSET
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1,1
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COMMENTS
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Or numbers n such that the smallest prime divisor of n^2+1 is A002313(9).
a(n)== 50 or 72 (mod 122).
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LINKS
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EXAMPLE
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194 is in the sequence because 194^2+1= 61*617.
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MATHEMATICA
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lst={}; Do[If[FactorInteger[n^2+1][[1, 1]]==61, AppendTo[lst, n]], {n, 2, 10000}]; lst
p = 61; ps = Select[Range[p - 1], Mod[#, 4] != 3 && PrimeQ[#] &]; Select[Range[8000], Divisible[(nn = #^2 + 1), p] && ! Or @@ Divisible[nn, ps] &] (* Amiram Eldar, Aug 16 2019 *)
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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