1
/**
2
 * @param {number} n
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 * @return {number}
4
 */
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var primePalindrome = function (n) {
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  while (true) {
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    let str = String(n);
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    if (String(n).length % 2 == 0 && n > 11) {
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      n = Math.pow(10, Math.ceil(Math.log10(n + 1)));
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      // or n = 1 + Array(str.length).fill(0).join("")
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      continue;
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    }
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    if (!isPalindrome(str)) {
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      n++;
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      continue;
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    }
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    if (isPrime(n)) return n;
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    n++;
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  }
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};
21

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function isPrime(n) {
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  if (n <= 1) return false;
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  if (n <= 3) return true;
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  if (n % 2 == 0 || n % 3 == 0) return false;
26

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  for (let i = 3; i <= Math.floor(Math.sqrt(n)) + 1; i += 2) {
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    if (n % i == 0) return false;
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  }
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  return true;
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}
32

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function isPalindrome(str) {
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  let l = 0,
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    r = str.length - 1;
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  while (l < r) {
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    if (str[l] != str[r]) return false;
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    l++;
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    r--;
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  }
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  return true;
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}