[Init]

.gitignore

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+.idea
+*.iml
+out

src/Main.java

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+import java.io.BufferedWriter;
+import java.io.FileWriter;
+import java.io.IOException;
+
+public class Main {
+
+  public static void main(String[] args) {
+    int n = 1_000_000_000; // Upper limit
+    boolean[] isPrime = new boolean[n + 1];
+
+    for (int i = 2; i <= n; i++) {
+      isPrime[i] = true;
+    }
+
+    for (int p = 2; p * p <= n; p++) {
+      if (isPrime[p]) {
+        for (int i = p * p; i <= n; i += p) {
+          isPrime[i] = false;
+        }
+      }
+    }
+
+    try (BufferedWriter writer = new BufferedWriter(new FileWriter("primes.txt"))) {
+      for (int i = 2; i <= n; i++) {
+        if (isPrime[i]) {
+          writer.write(Integer.toString(i));
+          writer.newLine();
+        }
+      }
+      System.out.println("Prime numbers up to " + n + " have been saved to primes.txt.");
+    } catch (IOException e) {
+      e.printStackTrace();
+    }
+  }
+}