Descending primes: Difference between revisions
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76543 76541 76421 75431 764321 83 863 853 821 8761 8753 8741 8731 8641 8543 8521 8431 87643 87641 87631 87541 87421 86531 876431 865321 8765321 8764321 97 983
971 953 941 9871 9851 9743 9721 9643 9631 9521 9431 9421 98731 98641 98621 98543 98321 97651 96431 94321 987631 987541 986543 975421 9875321 9754321 98765431 98764321 97654321</syntaxhighlight>
=={{header|Java}}==
<syntaxhighlight lang="java">
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public final class DescendingPrimes {
public static void main(String[] aArgs) {
List<Integer> allNumbersStrictlyDescendingDigits = new ArrayList<Integer>(512);
for ( int i = 1; i < 512; i++ ) {
int number = 0;
int temp = i;
int digit = 9;
while ( temp > 0 ) {
if ( temp % 2 == 1 ) {
number = number * 10 + digit;
}
temp >>= 1;
digit -= 1;
}
allNumbersStrictlyDescendingDigits.add(number);
}
Collections.sort(allNumbersStrictlyDescendingDigits);
int count = 0;
for ( int number : allNumbersStrictlyDescendingDigits ) {
if ( isPrime(number) ) {
System.out.print(String.format("%9d%s", number, ( ++count % 10 == 0 ? "\n" : " " )));
}
}
System.out.println(System.lineSeparator());
System.out.println("There are " + count + " descending primes.");
}
private static boolean isPrime(int aNumber) {
if ( aNumber < 2 || ( aNumber % 2 ) == 0 ) {
return aNumber == 2;
}
for ( int divisor = 3; divisor * divisor <= aNumber; divisor += 2 ) {
if ( aNumber % divisor == 0 ) {
return false;
}
}
return true;
}
}
</syntaxhighlight>
{{ out }}
<pre>
2 3 5 7 31 41 43 53 61 71
73 83 97 421 431 521 541 631 641 643
653 743 751 761 821 853 863 941 953 971
983 5431 6421 6521 7321 7541 7621 7643 8431 8521
8543 8641 8731 8741 8753 8761 9421 9431 9521 9631
9643 9721 9743 9851 9871 75431 76421 76541 76543 86531
87421 87541 87631 87641 87643 94321 96431 97651 98321 98543
98621 98641 98731 764321 865321 876431 975421 986543 987541 987631
8764321 8765321 9754321 9875321 97654321 98764321 98765431
There are 87 descending primes.
</pre>
=={{header|jq}}==
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