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National and Regional Contests
PEN Problems
PEN L Problems
2
L 2
L 2
Source:
May 25, 2007
number theory
greatest common divisor
Linear Recurrences
Problem Statement
The Fibonacci sequence
{
F
n
}
\{F_{n}\}
{
F
n
}
is defined by
F
1
=
1
,
F
2
=
1
,
F
n
+
2
=
F
n
+
1
+
F
n
.
F_{1}=1, \; F_{2}=1, \; F_{n+2}=F_{n+1}+F_{n}.
F
1
=
1
,
F
2
=
1
,
F
n
+
2
=
F
n
+
1
+
F
n
.
Show that
gcd
(
F
m
,
F
n
)
=
F
gcd
(
m
,
n
)
\gcd (F_{m}, F_{n})=F_{\gcd (m, n)}
g
cd
(
F
m
,
F
n
)
=
F
g
c
d
(
m
,
n
)
for all
m
,
n
∈
N
m, n \in \mathbb{N}
m
,
n
∈
N
.
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