70 lines
2.0 KiB
C++
70 lines
2.0 KiB
C++
#include <algorithm>
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#include <cstdint>
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#include <iomanip>
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#include <iostream>
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#include <vector>
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bool is_prime_type_3(const uint32_t& number) {
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if ( number < 2 ) return false;
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if ( number % 2 == 0 ) return false;
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if ( number % 3 == 0 ) return number == 3;
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for ( uint32_t divisor = 5; divisor * divisor <= number; divisor += 2 ) {
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if ( number % divisor == 0 ) { return false; }
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}
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return number % 4 == 3;
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}
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uint32_t least_prime_factor(const uint32_t& number) {
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if ( number == 1 ) { return 1; }
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if ( number % 3 == 0 ) { return 3; }
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if ( number % 5 == 0 ) { return 5; }
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for ( uint32_t divisor = 7; divisor * divisor <= number; divisor += 2 ) {
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if ( number % divisor == 0 ) { return divisor; }
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}
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return number;
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}
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int main() {
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uint32_t blums[50];
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uint32_t blum_count = 0;
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uint32_t last_digit_counts[10] = {};
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uint32_t number = 1;
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while ( blum_count < 400'000 ) {
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const uint32_t prime = least_prime_factor(number);
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if ( prime % 4 == 3 ) {
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const uint32_t quotient = number / prime;
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if ( quotient != prime && is_prime_type_3(quotient) ) {
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if ( blum_count < 50 ) {
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blums[blum_count] = number;
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}
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last_digit_counts[number % 10] += 1;
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blum_count += 1;
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if ( blum_count == 50 ) {
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std::cout << "The first 50 Blum integers:" << std::endl;
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for ( uint32_t i = 0; i < 50; ++i ) {
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std::cout << std::setw(3) << blums[i] << ( ( i % 10 == 9 ) ? "\n" : " " );
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}
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std::cout << std::endl;
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} else if ( blum_count == 26'828 || blum_count % 100'000 == 0 ) {
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std::cout << "The " << std::setw(6) << blum_count << "th Blum integer is: "
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<< std::setw(7) << number << std::endl;
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if ( blum_count == 400'000 ) {
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std::cout << "\n" << "Percent distribution of the first 400000 Blum integers:"
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<< std::endl;
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for ( const int32_t& i : { 1, 3, 7, 9 } ) {
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std::cout << " " << std::setw(6) << std::setprecision(5)
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<< (double) last_digit_counts[i] / 4'000 << "% end in " << i << std::endl;
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}
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}
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}
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}
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}
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number += ( number % 5 == 3 ) ? 4 : 2;
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}
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}
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