#include #include #include #include /* * Operations of power. * Header requirement: algorithm, vector, cmath */ class Power { typedef long long i64; public: /* a^b with no modulo operations */ static long long power(long long a, long long b) { i64 s = 1; i64 c = a; while (b > 0) { if (b % 2) { s *= c; } c *= c; b /= 2; } return s; } /* return (a,b) s.t, n = a^b and b is maximal. O(64) */ static std::pair toPower(long long n) { for (int i = 64; i >= 2; i--) { i64 app = std::pow(n, 1.0/i); for (int d = -4; d <= 4; d++) { i64 x = app + d; if (x <= 0) continue; if (power(x, i) == n) { return std::pair(x, i); } } } return std::pair(n, 1); } /* factorize n and returns prime factors and their exponents. O(sqrt(n)) */ static std::vector > factorize(long long n) { std::vector > res; i64 p = 2; int c = 0; while (n >= 1) { if (c == 0 && n < p * p) { if(n != 1) { res.push_back(std::pair(n,1)); } break; } if (n % p != 0) { if (c > 0) { res.push_back(std::pair(p,c)); } p++; c = 0; continue; } n /= p; c++; } return res; } /* * Euler's totient function. O(sqrt(n)) */ static long long totient(long long n) { std::vector > res = factorize(n); for (int i = 0; i < res.size(); ++i) { i64 p = res[i].first; n /= p; n *= p - 1; } return n; } }; #include #define REP(i,s,n) for(int i=(int)(s);i<(int)(n);i++) using namespace std; typedef long long int ll; typedef vector VI; typedef pair PI; const double EPS=1e-9; const ll mod = 1e9 + 7; ll invmod(ll x) { ll e = mod - 2; ll sum = 1; ll cur = x; while (e > 0) { if (e % 2) { sum = sum * cur % mod; } cur = cur * cur % mod; e /= 2; } return sum; } const int F = 1e6 + 10; ll ftbl[F]; const int K = 100100; int c[K]; int main(void){ ll tmp = 1; REP(i, 0, F) { ftbl[i] = tmp; tmp *= i + 1; tmp %= mod; } int k; cin >> k; int g = 0; int tot = 0; REP(i, 0, k) { cin >> c[i]; g = __gcd(g, c[i]); tot += c[i]; } ll cnt = 0; REP(f, 1, g + 1) { if (g % f != 0) { continue; } ll sum = ftbl[tot / f]; REP(i, 0, k) { sum *= invmod(ftbl[c[i] / f]); sum %= mod; } sum *= Power::totient(f); cnt += sum; cnt %= mod; } cnt *= invmod(tot); cnt %= mod; cout << cnt << endl; }