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APMO
2024 APMO
4
4
Part of
2024 APMO
Problems
(1)
NT is dead once again
Source: APMO 2024 P4
7/29/2024
Prove that for every positive integer
t
t
t
there is a unique permutation
a
0
,
a
1
,
…
,
a
t
−
1
a_0, a_1, \ldots , a_{t-1}
a
0
,
a
1
,
…
,
a
t
−
1
of
0
,
1
,
…
,
t
−
1
0, 1, \ldots , t-1
0
,
1
,
…
,
t
−
1
such that, for every
0
≤
i
≤
t
−
1
0 \leq i \leq t-1
0
≤
i
≤
t
−
1
, the binomial coefficient
(
t
+
i
2
a
i
)
\binom{t+i}{2a_i}
(
2
a
i
t
+
i
)
is odd and
2
a
i
≠
t
+
i
2a_i \neq t+i
2
a
i
=
t
+
i
.
number theory
combinatorics
APMO 2024