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A293958
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Smallest odd prime divisor of (2n+1)^2 + 1.
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2
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5, 13, 5, 41, 61, 5, 113, 5, 181, 13, 5, 313, 5, 421, 13, 5, 613, 5, 761, 29, 5, 1013, 5, 1201, 1301, 5, 17, 5, 1741, 1861, 5, 2113, 5, 2381, 2521, 5, 29, 5, 3121, 17, 5, 3613, 5, 17, 41, 5, 4513, 5, 13, 5101, 5, 37, 5, 13, 61, 5, 17, 5, 73, 7321, 5, 13, 5, 53, 8581, 5, 13, 5, 9661, 9941, 5
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OFFSET
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1,1
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COMMENTS
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If the map "x -> smallest odd prime divisor of n^2+1" is iterated, does it always terminate in the 2-cycle (5 <-> 13)? - Zoran Sunic, Oct 25 2017
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LINKS
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FORMULA
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MATHEMATICA
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sod[n_]:=With[{fi=FactorInteger[n]}, If[fi[[1, 1]]==2, fi[[2, 1]], fi[1, 1]]]; sod/@(Range[3, 151, 2]^2+1) (* Harvey P. Dale, Dec 23 2023 *)
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PROG
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(PARI) a(n) = factor((2*n+1)^2 + 1)[2, 1]; \\ Michel Marcus, Nov 04 2017
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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