The correct options are
a1=2 and anan−1=an−1an−2
Hence, a1,a2,a3,a4,a5,... are in G.P.
Let a2=x. Then for n=3, we have
i.e., the sequence is 2,x,x22,x34,x48,... with common ratio, r=x2
Also, x and x48 are integers.
So, if x is even, then only x48 will be an integer.
Hence, possible values of x are 4 and 6. (x≠2, as terms are distinct)
Hence, possible value of a5=448,648