OFFSET
1,1
COMMENTS
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
A027862 is a subsequence. - David A. Corneth, Nov 04 2017
LINKS
David A. Corneth, Table of n, a(n) for n = 1..10000
FORMULA
MATHEMATICA
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 *)
PROG
(PARI) a(n) = factor((2*n+1)^2 + 1)[2, 1]; \\ Michel Marcus, Nov 04 2017
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Nov 04 2017, following a suggestion from Zoran Sunic.
STATUS
approved