Created
December 26, 2018 17:35
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function isPrime(number) { | |
var index; | |
var limit = Math.ceil(Math.sqrt(number)); | |
// since the main loop generates odd numbers only | |
// we can start testing primality dividing by 3 | |
for (index = 3; index <= limit; index += 2) { | |
if (number % index === 0) { | |
return false; | |
} | |
} | |
return true; | |
} | |
function largestPrimeFactor(number) { | |
var factor = Math.ceil(Math.sqrt(number)); | |
// start with an odd number | |
factor = (factor & 1) === 0 ? factor - 1 : factor; | |
while (!(number % factor === 0 && isPrime(factor))) { | |
factor -= 2; // odd numbers only | |
} | |
return factor; | |
} | |
largestPrimeFactor(600851475143); |
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