markdown エラトステネスのふるいで双子素数を求める

Posted 2021-05-06

const n = parseInt(prompt('n'), 10);
const max = Math.floor(Math.sqrt(n));
const p = [];
for(let i=2; i<=n; i++) p[i] = true;
let x = 2;

while(x<=max) {
  for(let i=2*x; i<=n; i+=x) p[i] = false;
  while(!p[++x]) ;
}

for(let i=2; i<=n-2; i++) {
  if(p[i] && p[i+2]) {
    console.log(`${i}, ${i+2}`);
  }
}

JS-エラトステネスのふるいで双子素数を求める
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