Honaker primes: Difference between revisions
New post without using external libraries, in addition to an existing post which uses the "Primesieve" lexternal ibrary.
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(New post without using external libraries, in addition to an existing post which uses the "Primesieve" lexternal ibrary.) |
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Ten thousandth: (286069, 4043749)
</pre>
===Without external libraries===
<syntaxhighlight lang="c++">
#include <cstdint>
#include <iomanip>
#include <iostream>
#include <string>
#include <vector>
uint32_t honaker_index = 0;
uint32_t prime_index = 0;
std::vector<uint32_t> primes;
struct HonakerPrime {
uint32_t honaker_index, prime_index, prime;
std::string to_string() {
return "(" + std::to_string(honaker_index) + ": "
+ std::to_string(prime_index) + ", "
+ std::to_string(prime) + ")";
}
};
void sieve_primes(const uint32_t& limit) {
primes.emplace_back(2);
const uint32_t half_limit = ( limit + 1 ) / 2;
std::vector<bool> composite(half_limit);
for ( uint32_t i = 1, p = 3; i < half_limit; p += 2, ++i ) {
if ( ! composite[i] ) {
primes.emplace_back(p);
for ( uint32_t a = i + p; a < half_limit; a += p ) {
composite[a] = true;
}
}
}
}
uint32_t digital_sum(uint32_t number) {
uint32_t sum = 0;
while ( number > 0 ) {
sum += number % 10;
number /= 10;
}
return sum;
}
HonakerPrime nextHonakerPrime() {
honaker_index++;
prime_index++;
while ( digital_sum(prime_index) != digital_sum(primes[prime_index - 1]) ) {
prime_index++;
}
return HonakerPrime(honaker_index, prime_index, primes[prime_index - 1]);
}
int main() {
sieve_primes(5'000'000);
std::cout << "The first 50 Honaker primes (honaker index: prime index, prime):" << std::endl;
for ( uint32_t i = 1; i <= 50; ++i ) {
std::cout << std::setw(17) << nextHonakerPrime().to_string() << ( i % 5 == 0 ? "\n" : " " );
}
for ( uint32_t i = 51; i < 10'000; ++i ) {
nextHonakerPrime();
}
std::cout << "\n" << "The 10,000th Honaker prime is: " + nextHonakerPrime().to_string() << std::endl;
}
</syntaxhighlight>
{{ out }}
<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>
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