Question

155

JavaScript factorial prevent infinity

rated 0 times [ 161] [ 6] / answers: 1 / hits: 9018 / 11 Years ago, tue, january 14, 2014, 12:00:00

I have been using this function for calculating factorial numbers in JavaScript:

var f = [];

function factorial (n) {

  if (n == 0 || n == 1)

    return 1;

  if (f[n] > 0)

    return f[n];

  return f[n] = factorial(n-1) * n;

}

All seemed to be going well until I tried the number 500. It returned infinity.

Is there a way that I can prevent infinity as an answer?

Thank you.

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stacyl

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2 Years ago

answered 11 Years ago deonkalvinw · Accepted Answer

You indeed need to use bignumbers. With math.js you can do:

// configure math.js to work with enough precision to do our calculation

math.config({precision: 2000});



// evaluate the factorial using a bignumber value

var value = math.bignumber(500);

var result = math.factorial(value);



// output the results

console.log(math.format(result, {notation: 'fixed'}));

This will output:

1220136825991110068701238785423046926253574342803192842192413588385845373153881997605496447502203281863013616477148203584163378722078177200480785205159329285477907571939330603772960859086270429174547882424912726344305670173270769461062802310452644218878789465754777149863494367781037644274033827365397471386477878495438489595537537990423241061271326984327745715546309977202781014561081188373709531016356324432987029563896628911658974769572087926928871281780070265174507768410719624390394322536422605234945850129918571501248706961568141625359056693423813008856249246891564126775654481886506593847951775360894005745238940335798476363944905313062323749066445048824665075946735862074637925184200459369692981022263971952597190945217823331756934581508552332820762820023402626907898342451712006207714640979456116127629145951237229913340169552363850942885592018727433795173014586357570828355780158735432768888680120399882384702151467605445407663535984174430480128938313896881639487469658817504506926365338175055478128640000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000