Let n be a positive integer. We call a n-tuple (a1,...,an) of positive integers nice if
∙gcd(a1,...,an)=1, and
∙ai∣ai−1+ai+1, for all i=1,...,n (we define a0=an and an+1=a1 here).
Find the maximal possible value of the sum a1+...+an if (a1,...,an) is a nice n-tuple.