Blum integer: Difference between revisions
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<pre>
Same as Wren example.
</pre>
=={{header|C++}}==
<syntaxhighlight lang="java">
#include <algorithm>
#include <cstdint>
#include <iomanip>
#include <iostream>
#include <vector>
bool is_prime_type_3(const int32_t number) {
if ( number < 2 ) return false;
if ( number % 2 == 0 ) return false;
if ( number % 3 == 0 ) return number == 3;
for ( int divisor = 5; divisor * divisor <= number; divisor += 2 ) {
if ( number % divisor == 0 ) { return false; }
}
return number % 4 == 3;
}
int32_t least_prime_factor(const int32_t number) {
if ( number == 1 ) { return 1; }
if ( number % 3 == 0 ) { return 3; }
if ( number % 5 == 0 ) { return 5; }
for ( int divisor = 7; divisor * divisor <= number; divisor += 2 ) {
if ( number % divisor == 0 ) { return divisor; }
}
return number;
}
int main() {
int32_t blums[50];
int32_t blum_count = 0;
int32_t last_digit_counts[10] = {};
int32_t number = 1;
while ( blum_count < 400'000 ) {
const int32_t prime = least_prime_factor(number);
if ( prime % 4 == 3 ) {
const int32_t quotient = number / prime;
if ( quotient != prime && is_prime_type_3(quotient) ) {
if ( blum_count < 50 ) {
blums[blum_count] = number;
}
last_digit_counts[number % 10] += 1;
blum_count += 1;
if ( blum_count == 50 ) {
std::cout << "The first 50 Blum integers:" << std::endl;
for ( int32_t i = 0; i < 50; ++i ) {
std::cout << std::setw(3) << blums[i] << ( ( i % 10 == 9 ) ? "\n" : " " );
}
std::cout << std::endl;
} else if ( blum_count == 26'828 || blum_count % 100'000 == 0 ) {
std::cout << "The " << std::setw(6) << blum_count << "th Blum integer is: "
<< std::setw(7) << number << std::endl;
if ( blum_count == 400'000 ) {
std::cout << "\nPercent distribution of the first 400000 Blum integers:" << std::endl;
for ( const int32_t& i : { 1, 3, 7, 9 } ) {
std::cout << " " << std::setw(6) << std::setprecision(5)
<< (double) last_digit_counts[i] / 4'000 << "% end in " << i << std::endl;
}
}
}
}
}
number += ( number % 5 == 3 ) ? 4 : 2;
}
}
</syntaxhighlight>
{{ out }}
<pre>
The first 50 Blum integers:
21 33 57 69 77 93 129 133 141 161
177 201 209 213 217 237 249 253 301 309
321 329 341 381 393 413 417 437 453 469
473 489 497 501 517 537 553 573 581 589
597 633 649 669 681 713 717 721 737 749
The 26828th Blum integer is: 524273
The 100000th Blum integer is: 2075217
The 200000th Blum integer is: 4275533
The 300000th Blum integer is: 6521629
The 400000th Blum integer is: 8802377
Percent distribution of the first 400000 Blum integers:
25.001% end in 1
25.017% end in 3
24.997% end in 7
24.985% end in 9
</pre>
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