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A256970
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Smallest prime divisor of 4*n^2+1.
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5
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5, 17, 37, 5, 101, 5, 197, 257, 5, 401, 5, 577, 677, 5, 17, 5, 13, 1297, 5, 1601, 5, 13, 29, 5, 41, 5, 2917, 3137, 5, 13, 5, 17, 4357, 5, 13, 5, 5477, 53, 5, 37, 5, 7057, 13, 5, 8101, 5, 8837, 13, 5, 73, 5, 29, 17, 5, 12101, 5, 41, 13457, 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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REFERENCES
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Richard Friedberg, An Adventurer's Guide to Number Theory, McGraw-Hill, NY, 1968.
Popular Computing (Calabasas, CA), Friedberg's Sequence, Vol. 5 (No. 46, Jan 1977), page PC46-2.
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LINKS
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MATHEMATICA
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Table[FactorInteger[4*n^2+1][[1, 1]], {n, 59}] (* Ivan N. Ianakiev, Apr 20 2015 *)
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PROG
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(Haskell)
(PARI) a(n) = factor(4*n^2+1)[1, 1]; \\ Michel Marcus, Apr 20 2015
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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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