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7
2013 HMMT Guts #7: Divisors of 15!
2013 HMMT Guts #7: Divisors of 15!
Source:
March 26, 2013
HMMT
number theory
prime factorization
Problem Statement
Find the number of positive divisors
d
d
d
of
15
!
=
15
⋅
14
⋅
⋯
⋅
2
⋅
1
15!=15\cdot 14\cdot\cdots\cdot 2\cdot 1
15
!
=
15
⋅
14
⋅
⋯
⋅
2
⋅
1
such that
gcd
(
d
,
60
)
=
5
\gcd(d,60)=5
g
cd
(
d
,
60
)
=
5
.
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