Note that d(2) = 2,otherwise d(3),d(4) and d(5) are odd.Also d(3) > 6 ,so d(3) is prime.If d(4) is even ,then d(4)=2d(3) and d(5) is a multiple of 3,implying d(3)=3,contradiction.So d(4) must be prime and d(5) even.It follows that d(5) = 2d(3),from which we get that d(4) = d(3) + 6 and d(6) = 3d(3) - 1.But d(6) is even,implying d(6)=2d(4),so d(3) = 13 ,d(4) = 19,d(5)= 26 and d(6) = 38.The minimum n for which these are satisfied is 494