Data update

Task/Smarandache-Wellin-primes/Java/smarandache-wellin-primes.java

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+import java.math.BigInteger;
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+public final class SmarandacheWellinPrimes {
+
+	public static void main(String[] args) {
+		primes = listPrimesUpTo(12_000);
+		smarandacheWellinPrimes();
+		System.out.println();
+		derivedSmarandacheWellinPrimes();
+	}
+	
+	private static void smarandacheWellinPrimes() {
+		int count = 0;
+		int index = 1;
+		int number = 2;
+		String numberString = "2";
+		System.out.println("The first eight Smarandache-Wellin primes are:");
+		
+		while ( count < 8 ) {
+			if ( new BigInteger(numberString).isProbablePrime(CERTAINTY_LEVEL) ) {
+				count += 1;
+				System.out.println(String.format("%2d%s%-4d%s%-5d%s%d", count, ":  index = ", index,
+					"  last prime = ", number, "  number of digits = ", numberString.length()));
+			}			
+			
+			number = primes.get(index);
+			numberString += number;
+			index += 1;
+		}
+	}
+	
+	private static void derivedSmarandacheWellinPrimes() {		
+ 		int count = 0;
+		int index = 0;
+		int[] digitFrequencies = new int[10];
+		System.out.println("The first 20 derived Smarandache-Wellin numbers which are prime:");
+		
+		while ( count < 20 ) {
+			String prime = String.valueOf(primes.get(index));
+			for ( char ch : prime.toCharArray() ) {
+				digitFrequencies[ch - '0'] += 1;
+			}
+			
+			index += 1;
+			String joined = Arrays.stream(digitFrequencies).mapToObj(String::valueOf).collect(Collectors.joining(""));
+			if ( new BigInteger(joined).isProbablePrime(CERTAINTY_LEVEL) ) {
+				count += 1;
+				System.out.println(String.format("%2d%s%-4d%s%s", count, ":  index = ", index, "  prime = ", joined));
+			}
+		}
+	}
+	
+	private static List<Integer> listPrimesUpTo(int limit) {
+		final int halfLimit = ( limit + 1 ) / 2;
+		boolean[] composite = new boolean[halfLimit];
+		for ( int i = 1, p = 3; i < halfLimit; p += 2, i++ ) {
+			if ( ! composite[i] ) {
+				for ( int a = i + p; a < halfLimit; a += p ) {
+					composite[a] = true;
+				}
+			}
+		}
+		
+		List<Integer> result = Stream.of(2).limit(1).collect(Collectors.toList());
+		for ( int i = 1, p = 3; i < halfLimit; p += 2, i++ ) {
+			if ( ! composite[i] ) {
+				result.add(p);
+			}
+		}
+		return result;
+	}
+	
+	private static List<Integer> primes;
+	
+	private static final int CERTAINTY_LEVEL = 15;
+	
+}