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A294657
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Largest number in the orbit of n under iteration of the map A125256: x -> smallest odd prime divisor of n^2+1.
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4
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13, 13, 17, 13, 37, 13, 13, 421, 5101, 1861, 13, 13, 197, 113, 257, 17, 18, 16381, 401, 21, 22, 23, 577, 313, 677, 27, 28, 421, 30, 31, 32, 33, 34, 613, 1297, 37, 38, 761, 1601, 421, 42, 43, 44, 1013, 421, 47, 48, 1201, 421, 1301, 52, 53, 2917, 55, 3137, 57, 58, 1515541, 60
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OFFSET
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2,1
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COMMENTS
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The orbit (or trajectory) under A125256 appears to end in the cycle 5 -> 13 -> 5 -> etc. for any initial value n.
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LINKS
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MATHEMATICA
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Table[Max[NestWhileList[SelectFirst[FactorInteger[#^2+1][[All, 1]], OddQ]&, n, #!=13&]], {n, 2, 60}] (* Requires Mathematica version 10 or later *) (* Harvey P. Dale, May 04 2019 *)
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PROG
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(PARI) A294657(n, S=[n])={while(#S<#S=setunion(S, [n=A125256(n)]), ); vecmax(S)}
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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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