%N Least k > 1 that divides A260868(n) + 2^k - 2.
%C For all numbers N not listed in A260868, the least k > 1 that divides N + 2^k - 2 is equal to the least prime factor of N.
%C It appears that the range of this sequence is A267999. For example, 155 occurs first somewhat late for N = 2729. - Corrected by _Thomas Ordowski_, Oct 27 2018
%o (PARI) my(aa(n)=for(k=2,9e9,Mod(2,k)^k+n-2||return(k)));for(n=2,1e5,aa(n)==factor(n)[1,1]||print1(aa(n)","))
%A _M. F. Hasler_, Aug 11 2015