Prime Number Calculator - Sieve

by rishul matta

JavaScript

function prime (N) {
	let arr = [];
	for (let i = 0; i <= N; ++i) {
  	arr[i] = i;
  }
  
  
  for (let i = 2; i <= N; ++i) {
  	if (arr[i]) {
      	let counter = 2;
  			let p = arr[i];
        while (p*counter <= N) {
          
          delete arr[p*counter];
          counter++;
        }    
    }
  }  
  return arr;
  
}

a = prime(100)
b = {};
a.filter(nos => nos > 10).forEach( nos => b[nos] = true);

coPrime = Object.keys(a).filter((nos) => {
	key = parseInt(nos.split("").reverse().join(""));
  if (key == nos) {
  	return false;
  }
  return b[key];
})