Question
Question: The number of odd proper divisors of 3<sup>p</sup>. 6<sup>m</sup>.21<sup>n</sup> is-...
The number of odd proper divisors of 3p. 6m.21n is-
A
(p+1) (m+1) (n+1) – 2
B
(p + m + n + 1) (n + 1) –1
C
(p + 1) (m+1) (n+1) – 1
D
None of these
Answer
(p + m + n + 1) (n + 1) –1
Explanation
Solution
3p. 6m.21n = 2m.3p+m+n.7n
\ the required number of proper divisors
= Number of selections of any number of 3’sand 7’s
[Q for odd divisors 2 must not be selected]
= (p + m + n + 1) (n + 1) –1