Smarandache-Wellin primes: Difference between revisions
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19th: index 1087 prime 208614364610327343341589284471
20th: index 1188 prime 229667386663354357356628334581
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=={{header|Java}}==
<syntaxhighlight lang="java">
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;
}
</syntaxhighlight>
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<pre>
The first eight Smarandache-Wellin primes are:
1: index = 1 last prime = 2 number of digits = 1
2: index = 2 last prime = 3 number of digits = 2
3: index = 4 last prime = 7 number of digits = 4
4: index = 128 last prime = 719 number of digits = 355
5: index = 174 last prime = 1033 number of digits = 499
6: index = 342 last prime = 2297 number of digits = 1171
7: index = 435 last prime = 3037 number of digits = 1543
8: index = 1429 last prime = 11927 number of digits = 5719
The first 20 derived Smarandache-Wellin numbers which are prime:
1: index = 32 prime = 4194123321127
2: index = 72 prime = 547233879626521
3: index = 73 prime = 547233979727521
4: index = 134 prime = 13672766322929571043
5: index = 225 prime = 3916856106393739943689
6: index = 303 prime = 462696313560586013558131
7: index = 309 prime = 532727113760586013758133
8: index = 363 prime = 6430314317473636515467149
9: index = 462 prime = 8734722823685889120488197
10: index = 490 prime = 9035923128899919621189209
11: index = 495 prime = 9036023329699969621389211
12: index = 522 prime = 9337023533410210710923191219
13: index = 538 prime = 94374237357103109113243102223
14: index = 624 prime = 117416265406198131121272110263
15: index = 721 prime = 141459282456260193137317129313
16: index = 738 prime = 144466284461264224139325131317
17: index = 790 prime = 156483290479273277162351153339
18: index = 852 prime = 164518312512286294233375158359
19: index = 1087 prime = 208614364610327343341589284471
20: index = 1188 prime = 229667386663354357356628334581
</pre>
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