From fa2ead090f9aa51544733221c6494efd3abe8ab6 Mon Sep 17 00:00:00 2001
From: unlockable <gaogao174561@outlook.com>
Date: Mon, 25 Aug 2025 20:06:30 +0800
Subject: [PATCH] 20211a

---
 thu20211a_ans.cpp | 12 ++++++++++++
 thu20211a_gen.cpp | 47 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 59 insertions(+)
 create mode 100644 thu20211a_ans.cpp
 create mode 100644 thu20211a_gen.cpp

diff --git a/thu20211a_ans.cpp b/thu20211a_ans.cpp
new file mode 100644
index 0000000..9a61c0f
--- /dev/null
+++ b/thu20211a_ans.cpp
@@ -0,0 +1,12 @@
+#include <stdio.h>
+
+int ans[] = {
+    0,11,23,31,41,53,61,71,83,97,101,113,127,131,149,151,163,173,181,191,2011,211,223,233,241,251,263,271,281,293,307,311,3217,331,347,353,367,373,383,397,401,419,421,431,443,457,461,479,487,491,503,5113,521,5323,541,557,563,571,587,593,601,613,6211,631,641,653,661,673,683,691,701,719,727,733,743,751,761,773,787,797,809,811,821,839,8419,853,863,877,881,8923,907,911,929,937,941,953,967,971,983,991,1009
+};
+
+int main() {
+    int in;
+    scanf("%d", &in);
+    printf("%d", ans[in]);
+    return 0;
+}
\ No newline at end of file
diff --git a/thu20211a_gen.cpp b/thu20211a_gen.cpp
new file mode 100644
index 0000000..13f1070
--- /dev/null
+++ b/thu20211a_gen.cpp
@@ -0,0 +1,47 @@
+#include <stdio.h>
+
+int not_prime[1000000] = {0};
+// 0 -> prime, 1 -> prime
+
+int main() {
+    not_prime[0] = 1;
+    not_prime[1] = 1;
+    int i = 2;
+    while (i < 1000) {
+        if (not_prime[i] == 1) {
+            i++;
+            continue;
+        }
+        int cur = i * i;
+        while (cur < 1000000) {
+            not_prime[cur] = 1;
+            cur += i;
+        }
+        i++;
+    }
+
+    for (int n = 1; n <= 100; n++) {
+        bool found = false;
+        for (int i = 1; i <= 9999; i += 2) {
+            int cat = 0;
+            if (i < 10) {
+                cat = n * 10 + i;
+            } else if (i < 100) {
+                cat = n * 100 + i;
+            } else if (i < 1000) {
+                cat = n * 1000 + i;
+            } else {
+                cat = n * 10000 + i;
+            }
+            if (!not_prime[cat]) {
+                printf("%d,", cat);
+                found = true;
+                break;
+            }
+        }
+        if (!found) {
+            printf("\n%d failed\n", n);
+        }
+    }
+    return 0;
+}
\ No newline at end of file