NUmber of factors.

n=2p.3q

how many factors of n2 are smaller than n

(edit) but do not divide n?

18 Answers

62
Lokesh Verma ·

No.. it is quite close!

9
Celestine preetham ·

confirm the correctness sir!!!!!

9
Celestine preetham ·

let x be no of factors of n2 less than n
now 2x +1 =tot no of factors of n2 ( by symmetry no of factors>n = that<n)
ie 2X+1=(2p+1)(2q+1)

hence X=((2p+1)(2q+1)-1)/2

of this (q+1)(p+1) -1 are factors of n itself

so req ans is (3pq + p + q +1)/2 after subtraction and simplification

62
Lokesh Verma ·

OOps varun u caught me.. this should have been any factor of n2 which does not divide n :)

sorry dude :)
(edited the question accordingly!!)

But i guess we should try this one now :P

B.t.w ur answer for this part is correct :)

1
varun ·

Any number smaller than n is not divisible by n right ?

So any factor of n2 lass than n is not divisible by n right ?

62
Lokesh Verma ·

Did u read the question!
" are smaller than n but not divisible by n?"

1
varun ·

n = 25.30

n2 = 210

The number of factors of 1024 is 11.
Therefore the number of factors of n2 less than n is (11-1)/2 = 5.

5 + 0 + 2( 5 * 0) = 5

62
Lokesh Verma ·

Let's see p=5 and q=0

The answer should be 0 ?

1
varun ·

Lol I got that result by just seeing the different values for number of factors for n2 for different values of p and q.

So I can't be 100% sure.. but w/e value of p and q I substitute, I am getting the answer..

And the result is only for p≥0 and q≥0.

62
Lokesh Verma ·

No one solving this one? This is a good question! :)

1
varun ·

Is it

p+q+2pq ?

62
Lokesh Verma ·

HINT

Find the number of factors of n2 < n

Find the number of factors of n which are smaller than n!

Are all factors of n also factors of n2?

If u answer these three simple questions individually u will reach the answer :)

62
Lokesh Verma ·

(2p+1)(2q+1) - (q+1)(p+1) ??

No dear.. this is an obvious choice.. but unfortunately not the correct solution!

Ur giving this answer is obvious! but no! In an objective paper i am damn sure 1/2 th eppl wud have givne this as the answer :)

1
Anika Jain ·

(2p+1)(2q+1) - (q+1)(p+1) ??

62
Lokesh Verma ·

no buddy!

but still it wud be nice if we can disucss ur logic?

1
varun ·

4 + 3|p-q| ?

62
Lokesh Verma ·

yes

1
varun ·

smaller than n but not divisible by n

Any factor of n2smaller than n is not divisible by n right ?

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