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239 Open Math Olympiad
2024 239 Open Mathematical Olympiad
7
Weird sequence NT
Weird sequence NT
Source: 239 MO 2024 S7
May 22, 2024
number theory
Problem Statement
Let
n
>
3
n>3
n
>
3
be a positive integer satisfying
2
n
+
1
=
3
p
2^n+1=3p
2
n
+
1
=
3
p
, where
p
p
p
is a prime. Let
s
0
=
2
n
−
2
+
1
3
s_0=\frac{2^{n-2}+1}{3}
s
0
=
3
2
n
−
2
+
1
and
s
i
=
s
i
−
1
2
−
2
s_i=s_{i-1}^2-2
s
i
=
s
i
−
1
2
−
2
for
i
>
0
i>0
i
>
0
. Show that
p
∣
2
s
n
−
2
−
3
p \mid 2s_{n-2}-3
p
∣
2
s
n
−
2
−
3
.
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