The sieve of Sundaram: Difference between revisions
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The millionth odd prime number: 15485867
124.8262 ms</pre>P.S. for those (possibly faithless) who wish to have a conventional prime number generator, one can uncomment the <code>yield return 2</code> line at the top of the function.
=={{header|C++}}==
<syntaxhighlight lang="c++">
#include <cmath>
#include <cstdint>
#include <iomanip>
#include <iostream>
#include <vector>
std::vector<uint32_t> sieve_of_sundaram(const uint32_t& limit) {
std::vector<uint32_t> primes = {};
if ( limit < 3 ) {
return primes;
}
const uint32_t k = ( limit - 3 ) / 2 + 1;
std::vector<bool> marked(k, true);
for ( uint32_t i = 0; i < ( std::sqrt(limit) - 3 ) / 2 + 1; ++i ) {
uint32_t p = 2 * i + 3;
uint32_t s = ( p * p - 3 ) / 2;
for ( uint32_t j = s; j < k; j += p ) {
marked[j] = false;
}
}
for ( uint32_t i = 0; i < k; ++i ) {
if ( marked[i] ) {
primes.emplace_back(2 * i + 3);
}
}
return primes;
}
int main() {
std::vector<uint32_t> primes = sieve_of_sundaram(16'000'000);
std::cout << "The first 100 odd primes generated by the Sieve of Sundaram:" << std::endl;
for ( uint32_t i = 0; i < 100; ++i ) {
std::cout << std::setw(3) << primes[i] << ( i % 10 == 9 ? "\n" :" " );
}
std::cout << "\n" << "The 1_000_000th Sundaram prime is " << primes[1'000'000 - 1] << std::endl;
}
</syntaxhighlight>
{{ out }}
<pre>
The first 100 odd primes generated by the Sieve of Sundaram:
3 5 7 11 13 17 19 23 29 31
37 41 43 47 53 59 61 67 71 73
79 83 89 97 101 103 107 109 113 127
131 137 139 149 151 157 163 167 173 179
181 191 193 197 199 211 223 227 229 233
239 241 251 257 263 269 271 277 281 283
293 307 311 313 317 331 337 347 349 353
359 367 373 379 383 389 397 401 409 419
421 431 433 439 443 449 457 461 463 467
479 487 491 499 503 509 521 523 541 547
The 1_000_000th Sundaram prime is 15485867
</pre>
=={{header|F_Sharp|F#}}==
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