Codeforces Round #450 (Div. 2) D. Unusual Sequences 数学
Countthenumberofdistinctsequencesa1, a2, …, an(1 ≤ ai)consistingofpositiveintegerssuchthatgcd(a1, a2, …, an) = xand.Asthisnumbercouldbelarge,printtheanswermodulo109 + 7.gcdheremeansthegreatestcommondi