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2013 Nordic
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(1)
sequence that contains all positive rational numbers
Source: Nordic Mathematical Contest 2013 #3
9/23/2017
Define a sequence
(
n
k
)
k
≥
0
{(n_k)_{k\ge 0}}
(
n
k
)
k
≥
0
by
n
0
=
n
1
=
1
{n_{0 }= n_{1} = 1}
n
0
=
n
1
=
1
, and
n
2
k
=
n
k
+
n
k
−
1
{n_{2k} = n_k + n_{k-1} }
n
2
k
=
n
k
+
n
k
−
1
and
n
2
k
+
1
=
n
k
{n_{2k+1} = n_k}
n
2
k
+
1
=
n
k
for
k
≥
1
{k \ge 1}
k
≥
1
. Let further
q
k
=
n
k
{q_k = n_k }
q
k
=
n
k
/
n
k
−
1
{ n_{k-1} }
n
k
−
1
for each
k
≥
1
{k \ge 1}
k
≥
1
. Show that every positive rational number is present exactly once in the sequence
(
q
k
)
k
≥
1
{(q_k)_{k\ge 1}}
(
q
k
)
k
≥
1
Sequence
rational
number theory