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2020 BMT Fall
24
2020 BMT Team 24
2020 BMT Team 24
Source:
January 9, 2022
algebra
combinatorics
Problem Statement
For positive integers
N
N
N
and
m
m
m
, where
m
≤
N
m \le N
m
≤
N
, define
a
m
,
N
=
1
(
N
+
1
m
)
∑
i
=
m
−
1
N
−
1
(
i
m
−
1
)
N
−
i
a_{m,N} =\frac{1}{{N+1 \choose m}} \sum_{i=m-1}^{N-1} \frac{ {i \choose m-1}}{N - i}
a
m
,
N
=
(
m
N
+
1
)
1
i
=
m
−
1
∑
N
−
1
N
−
i
(
m
−
1
i
)
Compute the smallest positive integer
N
N
N
such that
∑
m
=
1
N
a
m
,
N
>
2020
N
N
+
1
\sum^N_{m=1}a_{m,N} >\frac{2020N}{N +1}
m
=
1
∑
N
a
m
,
N
>
N
+
1
2020
N
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