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%I #28 Dec 23 2023 14:39:40
%S 5,13,5,41,61,5,113,5,181,13,5,313,5,421,13,5,613,5,761,29,5,1013,5,
%T 1201,1301,5,17,5,1741,1861,5,2113,5,2381,2521,5,29,5,3121,17,5,3613,
%U 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
%N Smallest odd prime divisor of (2n+1)^2 + 1.
%C 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
%C A027862 is a subsequence. - _David A. Corneth_, Nov 04 2017
%H David A. Corneth, <a href="/A293958/b293958.txt">Table of n, a(n) for n = 1..10000</a>
%F a(n) = A078701(A069894(n)). - _Michel Marcus_, Nov 04 2017
%t 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 *)
%o (PARI) a(n) = factor((2*n+1)^2 + 1)[2,1]; \\ _Michel Marcus_, Nov 04 2017
%Y A bisection of A125256. Cf. A027862, A069894, A078701, A256970.
%K nonn
%O 1,1
%A _N. J. A. Sloane_, Nov 04 2017, following a suggestion from _Zoran Sunic_.
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