Data commit

Task/Totient-function/D/totient-function.d

@@ -0,0 +1,52 @@
+import std.stdio;
+
+int totient(int n) {
+    int tot = n;
+
+    for (int i = 2; i * i <= n; i += 2) {
+        if (n % i == 0) {
+            while (n % i == 0) {
+                n /= i;
+            }
+            tot -= tot / i;
+        }
+        if (i==2) {
+            i = 1;
+        }
+    }
+
+    if (n > 1) {
+        tot -= tot / n;
+    }
+    return tot;
+}
+
+void main() {
+    writeln(" n    φ   prime");
+    writeln("---------------");
+
+    int count = 0;
+    for (int n = 1; n <= 25; n++) {
+        int tot = totient(n);
+
+        if (n - 1 == tot) {
+            count++;
+        }
+
+        writefln("%2d   %2d   %s", n,tot, n - 1 == tot);
+    }
+    writeln;
+
+    writefln("Number of primes up to %6d = %4d", 25, count);
+    for (int n = 26; n <= 100_000; n++) {
+        int tot = totient(n);
+
+        if (n - 1 == tot) {
+            count++;
+        }
+
+        if (n == 100 || n == 1_000 || n % 10_000 == 0) {
+            writefln("Number of primes up to %6d = %4d", n, count);
+        }
+    }
+}