Strong and weak primes: Difference between revisions

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   weak primes below   1,000,000: 37,780
   weak primes below  10,000,000: 321,750
+</pre>
+=={{header|AWK}}==
+<lang AWK>
+# syntax: GAWK -f STRONG_AND_WEAK_PRIMES.AWK
+BEGIN {
+    for (i=1; i<1E7; i++) {
+      if (is_prime(i)) {
+        arr[++n] = i
+      }
+    }
+# strong:
+    stop1 = 36 ; stop2 = 1E6 ; stop3 = 1E7
+    count1 = count2 = count3 = 0
+    printf("The first %d strong primes:",stop1)
+    for (i=2; count1<stop1; i++) {
+      if (arr[i] > (arr[i-1] + arr[i+1]) / 2) {
+        count1++
+        printf(" %d",arr[i])
+      }
+    }
+    printf("\n")
+    for (i=2; i<stop3; i++) {
+      if (arr[i] > (arr[i-1] + arr[i+1]) / 2) {
+        count3++
+        if (arr[i] < stop2) {
+          count2++
+        }
+      }
+    }
+    printf("Number below %d: %d\n",stop2,count2)
+    printf("Number below %d: %d\n",stop3,count3)
+# weak:
+    stop1 = 37 ; stop2 = 1E6 ; stop3 = 1E7
+    count1 = count2 = count3 = 0
+    printf("The first %d weak primes:",stop1)
+    for (i=2; count1<stop1; i++) {
+      if (arr[i] < (arr[i-1] + arr[i+1]) / 2) {
+        count1++
+        printf(" %d",arr[i])
+      }
+    }
+    printf("\n")
+    for (i=2; i<stop3; i++) {
+      if (arr[i] < (arr[i-1] + arr[i+1]) / 2) {
+        count3++
+        if (arr[i] < stop2) {
+          count2++
+        }
+      }
+    }
+    printf("Number below %d: %d\n",stop2,count2)
+    printf("Number below %d: %d\n",stop3,count3)
+    exit(0)
+}
+function is_prime(n,  d) {
+    d = 5
+    if (n < 2) { return(0) }
+    if (n % 2 == 0) { return(n == 2) }
+    if (n % 3 == 0) { return(n == 3) }
+    while (d*d <= n) {
+      if (n % d == 0) { return(0) }
+      d += 2
+      if (n % d == 0) { return(0) }
+      d += 4
+    }
+    return(1)
+}
+</lang>
+{{out}}
+<pre>
+The first 36 strong primes: 11 17 29 37 41 59 67 71 79 97 101 107 127 137 149 163 179 191 197 223 227 239 251 269 277 281 307 311 331 347 367 379 397 419 431 439
+Number below 1000000: 37723
+Number below 10000000: 320992
+The first 37 weak primes: 3 7 13 19 23 31 43 47 61 73 83 89 103 109 113 131 139 151 167 181 193 199 229 233 241 271 283 293 313 317 337 349 353 359 383 389 401
+Number below 1000000: 37781
+Number below 10000000: 321750
 </pre>