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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 is B.
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Detailed Solution
3p.6m.21n=2m.3p+m+n.7n ∴ The required number of proper divisors = Number of selection of any number of 3’s and 7’s [∴ for odd divisors 2 must not be selected]=(p+m+n+1)(n+1)−1 .