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National and Regional Contests
PEN Problems
PEN N Problems
10
N 10
N 10
Source:
May 25, 2007
More Sequences
Problem Statement
Let
a
,
b
a,b
a
,
b
be integers greater than 2. Prove that there exists a positive integer
k
k
k
and a finite sequence
n
1
,
n
2
,
…
,
n
k
n_1, n_2, \dots, n_k
n
1
,
n
2
,
…
,
n
k
of positive integers such that
n
1
=
a
n_1 = a
n
1
=
a
,
n
k
=
b
n_k = b
n
k
=
b
, and
n
i
n
i
+
1
n_i n_{i+1}
n
i
n
i
+
1
is divisible by
n
i
+
n
i
+
1
n_i + n_{i+1}
n
i
+
n
i
+
1
for each
i
i
i
(
1
≤
i
<
k
1 \leq i < k
1
≤
i
<
k
).
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