#include using namespace std; int main() { int N; cin >> N; int M = 200'000; int A[N+1]; for (int i = 1; i <= N; i++) cin >> A[i]; vector> C(M+1); for (int i = 1; i <= N; i++) { int d = 1; while(A[i] - d * i >= -M) { C[d].push_back(A[i] - d * i); d++; } } long long ans = 0; for (int d = 1; d <= M; d++) { map cnt; for (int x : C[d]) cnt[x]++; for (auto[x, c] : cnt) { if (x == 0) { ans += c * (c-1) / 2; } if (x < 0) { if (cnt.contains(-x)) ans += c * cnt[-x]; } } } cout << ans << endl; }