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Contests
International Contests
IMO Longlists
1987 IMO Longlists
25
d(m,n) are integers
d(m,n) are integers
Source:
September 5, 2010
induction
number theory unsolved
number theory
Problem Statement
Numbers
d
(
n
,
m
)
d(n,m)
d
(
n
,
m
)
, with
m
,
n
m, n
m
,
n
integers,
0
≤
m
≤
n
0 \leq m \leq n
0
≤
m
≤
n
, are defined by
d
(
n
,
0
)
=
d
(
n
,
n
)
=
0
d(n, 0) = d(n, n) = 0
d
(
n
,
0
)
=
d
(
n
,
n
)
=
0
for all
n
≥
0
n \geq 0
n
≥
0
and
m
d
(
n
,
m
)
=
m
d
(
n
−
1
,
m
)
+
(
2
n
−
m
)
d
(
n
−
1
,
m
−
1
)
for all
0
<
m
<
n
.
md(n,m) = md(n-1,m)+(2n-m)d(n-1,m-1) \text{ for all } 0 < m < n.
m
d
(
n
,
m
)
=
m
d
(
n
−
1
,
m
)
+
(
2
n
−
m
)
d
(
n
−
1
,
m
−
1
)
for all
0
<
m
<
n
.
Prove that all the
d
(
n
,
m
)
d(n,m)
d
(
n
,
m
)
are integers.
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