My Math Forum how to find number of factors of a number ?

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 August 22nd, 2013, 10:37 AM #1 Math Team     Joined: Jul 2013 From: काठमाडौं, नेपाल Posts: 872 Thanks: 60 Math Focus: सामान्य गणित how to find number of factors of a number ? also how to find the sum of the factors ?
 August 22nd, 2013, 12:04 PM #2 Senior Member   Joined: Mar 2012 From: Belgium Posts: 653 Thanks: 11 Re: how to find number of factors of a number ? There is not an obvious solution for this. What you should do is factorize your number and count them or add them.
August 22nd, 2013, 12:20 PM   #3
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Re: how to find number of factors of a number ?

Quote:
 Originally Posted by gelatine1 There is not an obvious solution for this. What you should do is factorize your number and count them or add them.
i think thats an absurd idea.

 August 22nd, 2013, 12:52 PM #4 Senior Member   Joined: Mar 2012 From: Belgium Posts: 653 Thanks: 11 Re: how to find number of factors of a number ? Imagine a prime number. according to you it must be easier then factorizing your number to determine the amount of it's prime factors. Well then it should be easy to determine that it's amount of prime factors is 1 and is a prime. I hope that you know that it is not that easy to determine if a number is prime or not. Or something else. Imagine 21 and 23. Is there anything about these numbers that tell you that one of them has 2 prime factors and the other only one ? No.
 August 22nd, 2013, 01:03 PM #5 Math Team     Joined: Jul 2013 From: काठमाडौं, नेपाल Posts: 872 Thanks: 60 Math Focus: सामान्य गणित Re: how to find number of factors of a number ? suppose i've a number 900, i would take me very long time to search each and every factor of this num. isn't there any quick way, may be some formulas ??
 August 22nd, 2013, 01:33 PM #6 Newbie   Joined: Nov 2011 Posts: 26 Thanks: 0 Re: how to find number of factors of a number ? If a formula is all you need there is one.. Let the number concerned be $N$, if it prime factorisation is $(A^a)(B^b)(C^c)...$ then it has $(a+1)(b+1)(c+1)...$ factors i.e you multiply the powers of its prime factors after adding one as per formula.. Hope you understand me
 August 22nd, 2013, 01:53 PM #7 Math Team     Joined: Jul 2013 From: काठमाडौं, नेपाल Posts: 872 Thanks: 60 Math Focus: सामान्य गणित Re: how to find number of factors of a number ? mr. monster i hope i'll understand that by the end of the century
 August 22nd, 2013, 02:09 PM #8 Newbie   Joined: Nov 2011 Posts: 26 Thanks: 0 Re: how to find number of factors of a number ? For example lets taake N to be 18; $18= 2 * 3^2$ we take the product of the expoents of the factors plus one The exponent of $2$is$1$ and the exponent of$3$ is $2$ Hence the number of divisors is $(1+1)*(2+1)= 6$ Hope now u understand
August 22nd, 2013, 02:14 PM   #9
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Re: how to find number of factors of a number ?

Quote:
 Originally Posted by MathMonster For example lets taake N to be 18; $18= 2 * 3^2$ we take the product of the expoents of the factors plus one The exponent of $2$is$1$ and the exponent of$3$ is $2$ Hence the number of divisors is $(1+1)*(2+1)= 6$ Hope now u understand
Oh I thought this problem was only about finding it's prime factors. and not about all factors. but anyway We still need to factorize our number.
And by the way finding the prime factors of 900 is not really a hard thing to do... $900=2^2*3^2*5^2$

 August 22nd, 2013, 02:17 PM #10 Math Team     Joined: Jul 2013 From: काठमाडौं, नेपाल Posts: 872 Thanks: 60 Math Focus: सामान्य गणित Re: how to find number of factors of a number ? i think i get it now, if i've, num = 2^3 * 5^4 * 3^3 num of fac = (3+1)(4+1)(3+1) is it so ?

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