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7
Find a such that each digit of n(n+1)/2 equals a
Find a such that each digit of n(n+1)/2 equals a
Source:
September 23, 2010
modular arithmetic
number theory
Digits
equation
IMO Shortlist
Problem Statement
For which digits
a
a
a
do exist integers
n
≥
4
n \geq 4
n
≥
4
such that each digit of
n
(
n
+
1
)
2
\frac{n(n+1)}{2}
2
n
(
n
+
1
)
equals
a
?
a \ ?
a
?
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