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2023 MOAA
14
2023 MOAA Team P14
2023 MOAA Team P14
Source:
October 14, 2023
MOAA 2023
Problem Statement
For a positive integer
n
n
n
, let function
f
(
n
)
f(n)
f
(
n
)
denote the number of positive integers
a
≤
n
a\leq n
a
≤
n
such that
gcd
(
a
,
n
)
=
gcd
(
a
+
1
,
n
)
=
1
\gcd(a,n) = \gcd(a+1,n) = 1
g
cd
(
a
,
n
)
=
g
cd
(
a
+
1
,
n
)
=
1
. Find the sum of all
n
n
n
such that
f
(
n
)
=
15
f(n)=15
f
(
n
)
=
15
.Proposed by Harry Kim
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