Dear Seqfans, Who is able to proof or find counter-sample following conjecture Quintic polynomial: (4 k - k^2 + 5 k^2 x + (20 k - 20 k^2) x^3 + (16 - 32 k + 16 k^2) x^5 is factorizable if and only when k belonging to finite set {2,4,243} no more such k up to k=10^7 Who have any idea let me know Best wishes Artur