Honaker primes: Difference between revisions

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Task example:<syntaxhighlight lang=J> (>: j. p:) 5 10$I.honk i.1e3

32j131 56j263 88j457 175j1039 176j1049 182j1091 212j1301 218j1361 227j1433 248j1571

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761j5801 767j5843 779j5927 820j6301 821j6311 826j6343 827j6353 847j6553 848j6563 857j6653</syntaxhighlight>

Here, we test the first thousand primes to see which are prime indices of Honaker primes. Then <code>I.</code>converts the test results back to index form, and <code>5 10$I.</code> organizes those indices in 5 rows of 10 columns (discarding any extra). Finally, we use complex number notation to form pairs of the corresponding honaker index and prime.

=={{header|Java}}==

import java.util.ArrayList;

import java.util.List;

import java.util.stream.Collectors;

import java.util.stream.IntStream;

public final class HonakerPrimes {

public static void main(String[] args) {

sievePrimes(5_000_000);

System.out.println("The first 50 Honaker primes (honaker index: prime index, prime):");

for ( int i = 1; i <= 50; i++ ) {

System.out.print(String.format("%17s%s", nextHonakerPrime(), ( i % 5 == 0 ? "\n" : " " ) ));

}

for ( int i = 51; i < 10_000; i++ ) {

nextHonakerPrime();

}

System.out.println();

System.out.println("The 10,000th Honaker prime is: " + nextHonakerPrime());

}

private static HonakerPrime nextHonakerPrime() {

honakerIndex += 1;

primeIndex += 1;

while ( digitalSum(primeIndex) != digitalSum(primes.get(primeIndex - 1)) ) {

primeIndex += 1;

}

return new HonakerPrime(honakerIndex, primeIndex, primes.get(primeIndex - 1));

}

private static int digitalSum(int number) {

return String.valueOf(number).chars().map( i -> i - (int) '0' ).sum();

}

private static void sievePrimes(int limit) {

List<Boolean> markedPrime = IntStream.range(0, limit).boxed().map( i -> true ).collect(Collectors.toList());

for ( int p = 2; p * p < limit; p++ ) {

if ( markedPrime.get(p) ) {

for ( int i = p * p; i < limit; i += p ) {

markedPrime.set(i, false);

}

primes = new ArrayList<Integer>();

for ( int p = 2; p < limit; p++ ) {

if ( markedPrime.get(p) ) {

primes.add(p);

}

private static int honakerIndex = 0;

private static int primeIndex = 0;

private static List<Integer> primes;

private static record HonakerPrime(int honakerIndex, int primeIndex, int prime) {

public String toString() {

return "(" + honakerIndex + ": " + primeIndex + ", " + prime + ")";

}

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</syntaxhighlight>

<pre>

The first 50 Honaker primes (honaker index: prime index, prime):

(1: 32, 131) (2: 56, 263) (3: 88, 457) (4: 175, 1039) (5: 176, 1049)

(6: 182, 1091) (7: 212, 1301) (8: 218, 1361) (9: 227, 1433) (10: 248, 1571)

(11: 293, 1913) (12: 295, 1933) (13: 323, 2141) (14: 331, 2221) (15: 338, 2273)

(16: 362, 2441) (17: 377, 2591) (18: 386, 2663) (19: 394, 2707) (20: 397, 2719)

(21: 398, 2729) (22: 409, 2803) (23: 439, 3067) (24: 446, 3137) (25: 457, 3229)

(26: 481, 3433) (27: 499, 3559) (28: 508, 3631) (29: 563, 4091) (30: 571, 4153)

(31: 595, 4357) (32: 599, 4397) (33: 635, 4703) (34: 637, 4723) (35: 655, 4903)

(36: 671, 5009) (37: 728, 5507) (38: 751, 5701) (39: 752, 5711) (40: 755, 5741)

(41: 761, 5801) (42: 767, 5843) (43: 779, 5927) (44: 820, 6301) (45: 821, 6311)

(46: 826, 6343) (47: 827, 6353) (48: 847, 6553) (49: 848, 6563) (50: 857, 6653)

The 10,000th Honaker prime is: (10000: 286069, 4043749)

</pre>

=={{header|jq}}==