Data commit

Task/Circular-primes/AWK/circular-primes.awk

@@ -0,0 +1,46 @@
+# syntax: GAWK -f CIRCULAR_PRIMES.AWK
+BEGIN {
+    p = 2
+    printf("first 19 circular primes:")
+    for (count=0; count<19; p++) {
+      if (is_circular_prime(p)) {
+        printf(" %d",p)
+        count++
+      }
+    }
+    printf("\n")
+    exit(0)
+}
+function cycle(n,  m,p) { # E.G. if n = 1234 returns 2341
+    m = n
+    p = 1
+    while (m >= 10) {
+      p *= 10
+      m /= 10
+    }
+    return int(m+10*(n%p))
+}
+function is_circular_prime(p,  p2) {
+    if (!is_prime(p)) {
+      return(0)
+    }
+    p2 = cycle(p)
+    while (p2 != p) {
+      if (p2 < p || !is_prime(p2)) {
+        return(0)
+      }
+      p2 = cycle(p2)
+    }
+    return(1)
+}
+function is_prime(x,  i) {
+    if (x <= 1) {
+      return(0)
+    }
+    for (i=2; i<=int(sqrt(x)); i++) {
+      if (x % i == 0) {
+        return(0)
+      }
+    }
+    return(1)
+}