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National and Regional Contests
Romania Contests
District Olympiad
2005 District Olympiad
1
digits
digits
Source:
March 5, 2005
AMC
AIME
USA(J)MO
USAMO
modular arithmetic
LaTeX
binomial coefficients
Problem Statement
Prove that for all
a
∈
{
0
,
1
,
2
,
…
,
9
}
a\in\{0,1,2,\ldots,9\}
a
∈
{
0
,
1
,
2
,
…
,
9
}
the following sum is divisible by 10:
S
a
=
a
‾
2005
+
1
a
‾
2005
+
2
a
‾
2005
+
⋯
+
9
a
‾
2005
.
S_a = \overline{a}^{2005} + \overline{1a}^{2005} + \overline{2a}^{2005} + \cdots + \overline{9a}^{2005}.
S
a
=
a
2005
+
1
a
2005
+
2
a
2005
+
⋯
+
9
a
2005
.
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