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# What is the sum of all the factors of 12972960

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SVP
Joined: 05 Jul 2006
Posts: 1516
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What is the sum of all the factors of 12972960 [#permalink]  12 Sep 2006, 11:16
What is the sum of all the factors of 12972960?
SVP
Joined: 05 Jul 2006
Posts: 1516
Followers: 5

Kudos [?]: 126 [0], given: 39

[#permalink]  12 Sep 2006, 13:13
anyone..... it is a good to know??
VP
Joined: 02 Jun 2006
Posts: 1266
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[#permalink]  12 Sep 2006, 14:07
Yezz,
Based on your problem I went out researching and found some interesting things. Suffice to say I second your statement about this being useful...

Ok.. given any number n we define the following functions:

a. D(n) := the total number of +ve divisors of n

b. σk(n) := the divisor function, which is the sum of the k-th powers of all the positive divisors of n

Specifically by definition :
* σ0(n) = d(n) (k = 0)
* σ1(n) = σ(n), (k = 1)

Both these functions are multiplicative i.e.

D(a x b) = D(a) x D(b) &
σk(a x b) = σk(a) x σk(b)

For example:
144 = 12 x 12
= 2x2x3 x 2x2x3
= 2^4 x 3^2

Therefore D(n) = # of +ve divisors of 144
= D(144) = σ0(2^4 x 3^2)
= σ0(2^4) x σ0(3^2)
= (1^0 + 2^0+4^0+8^0+16^0) x (1^0 + 3^0 +9^0)
= 5 x 3
= 15

Therefore total number of divisors of 144 = 15.

Similarly sum of all the divisors of 144 = σ1(144)
= σ1(2^4 x 3^2)
= σ1(2^4) x σ1(3^2)
= (1^1 + 2^1+4^1+8^1+16^1) x (1^1 + 3^1 + 9^1)
= 31 x 13 = 403

For the given problem the number 1297296 = 2^4 x 3^4 x 7 x 11 x 13

Therefore sum of divisors = σ1(2^4 x 3^4 x 7x11x13)
= σ1(2^4) x σ1(3^4) x σ1(7) x σ1(11)xσ1(13)
= (1^1+2^1+4^1+8+1+16^1) x (1^1+3^1+9^1+27^1+81^1)
x (1^1+7^1) x (1^1 +11^1)x(1^1+13^1)
= 31 x 121 x 8x 12x14
= 5041344

FYI the number of divisors of 1297296 = σ0(2^4 x 3^4 x 7x11x13) = 5 x 5 x 2 x 2 x 2= 200.

FYI: http://en.wikipedia.org/wiki/Multiplicative_function
SVP
Joined: 05 Jul 2006
Posts: 1516
Followers: 5

Kudos [?]: 126 [0], given: 39

[#permalink]  13 Sep 2006, 01:14
Hi Haas thanks a lot for the support and effort you did.

My aim is to show a very new concept ( at least to myself) to calculate the sum of all the factors of a certain intiger as above.

1) Find all the prime factors for this intiger

say it is (a^x*b^y*c*z...etc)

the sum of all the factors can be calculated through this formula

(a^(x+1) - 1)/(a-1) * (b^(y+1) - 1)/(b-1) * (c^(z+1) - 1)/(c-1)

2) to find the total count (number of factors ) of any intiger including (1, the intiger itself) can be calcultated through the following formula

(x+1) * (y+1) * (z+1)

Hope this helps
[#permalink] 13 Sep 2006, 01:14
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# What is the sum of all the factors of 12972960

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