Data commit

Task/Truncatable-primes/FreeBASIC/truncatable-primes-1.basic

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+' FB 1.05.0 Win64
+
+Function isPrime(n As Integer) As Boolean
+  If n Mod 2 = 0 Then Return n = 2
+  If n Mod 3 = 0 Then Return n = 3
+  Dim d As Integer = 5
+  While d * d <= n
+    If n Mod d = 0 Then Return False
+    d += 2
+    If n Mod d = 0 Then Return False
+    d += 4
+  Wend
+  Return True
+End Function
+
+Dim As UInteger i, j, p, pow, lMax = 2, rMax = 2
+Dim s As String
+
+' largest left truncatable prime less than 1000000
+' It can't end with 1, 4, 6, 8 or 9 as these numbers are not prime
+' Nor can it end in 2 if it has more than one digit as such a number would divide by 2
+For i = 3 To 999997 Step 2
+  s = Str(i)
+  If Instr(s, "0") > 1 Then Continue For '' cannot contain 0
+  j = s[Len(s) - 1] - 48
+  If j = 1 OrElse j = 9 Then Continue For
+  p = i
+  pow = 10 ^ (Len(s) - 1)
+  While pow > 1
+    If Not isPrime(p) Then Continue For
+    p Mod= pow
+    pow \= 10
+  Wend
+  lMax = i
+Next
+
+' largest right truncatable prime less than 1000000
+' It can't begin with 1, 4, 6, 8 or 9 as these numbers are not prime
+For i = 3 To 799999 Step 2
+  s = Str(i)
+  If Instr(s, "0") > 1 Then Continue For '' cannot contain 0
+  j = s[0] - 48
+  If j = 1 OrElse j = 4 OrElse j = 6 Then Continue For
+  p = i
+  While p > 0
+    If Not isPrime(p) Then Continue For
+    p \= 10
+  Wend
+  rMax = i
+Next
+
+Print "Largest left  truncatable prime : "; lMax
+Print "Largest right truncatable prime : "; rMax
+Print
+Print "Press any key to quit"
+Sleep

Task/Truncatable-primes/FreeBASIC/truncatable-primes-2.basic

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+' version 10-12-2016
+' compile with: fbc -s console
+
+Dim Shared As Byte isPrime()
+
+Sub sieve(m As UInteger)
+
+    Dim As Integer i, j
+    ReDim isPrime(m)
+
+    For i = 4 To m Step 2
+        isPrime(i) = 1
+    Next
+
+    For i = 3 To Sqr(m) Step 2
+        If isPrime(i) = 0 Then
+            For j = i * i To m Step i * 2
+                isPrime(j) = 1
+            Next
+        End If
+    Next
+
+End Sub
+
+' ------=< MAIN >=------
+
+#Define max 1000000 'upto 2^30 max for 32bit OS
+
+Dim As UInteger a(), lt_prime(5000), rt_prime(100)
+Dim As UInteger i, j, j1, p1, p2, left_max, right_max
+
+sieve(max)
+
+' left truncatable primes
+' if odd and ends with 3 or 7, never ends 1 or 9 (no prime
+' never ends on a 2 or 5 and starts with 1 to 9
+lt_prime(1) = 3 : lt_prime(2) = 7
+p1 = 1 : p2 = 2
+
+Do
+    For i = 1 To 9
+        j = Val( Str(i) + Str(lt_prime(p1)) )
+        If j > max Then Exit Do
+        If isPrime(j) = 0 Then ' if prime then add to the list
+            p2 += 1
+            lt_prime(p2) = j
+            If Left_max < j Then left_max = j
+        End If
+    Next
+    p1 += 1
+Loop Until p1 > p2   ' no more numbers to process
+
+' right truncatable prime
+' start with 2, 3, 5 or 7 and end with 1, 3, 7 or 9
+rt_prime(1) = 2 : rt_prime(2) = 3 : rt_prime(3) = 5 : rt_prime(4) = 7
+p1 = 1 : p2 = 4
+Dim As UInteger end_num(1 To 4) => {1, 3, 7, 9}
+
+Do
+    j1 = rt_prime(p1) * 10
+    If j1 > max Then Exit Do
+    For i = 1 To 4
+        j = j1 + End_num(i)
+        If isprime(j) = 0 Then  ' if prime then add to the list
+            p2 += 1
+            rt_prime(p2) = j
+           ' If right_max < j Then right_max = j
+        End If
+    Next
+    p1 += 1
+Loop Until p1 > p2   ' no more numbers to process
+' the last one added is the biggest
+right_max = rt_prime(p2)
+
+Print
+Print "The biggest  left truncatable prime below"; max; " is "; left_max
+Print "The biggest right truncatable prime below"; max; " is "; right_max
+
+' empty keyboard buffer
+While Inkey <> "" : Wend
+Print : Print "hit any key to end program"
+Sleep
+End