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Problems
Contests
National and Regional Contests
PEN Problems
PEN I Problems
2
2
Part of
PEN I Problems
Problems
(1)
I 2
Source:
5/25/2007
Prove that for any positive integer
n
n
n
,
⌊
n
3
⌋
+
⌊
n
+
2
6
⌋
+
⌊
n
+
4
6
⌋
=
⌊
n
2
⌋
+
⌊
n
+
3
6
⌋
.
\left\lfloor \frac{n}{3}\right\rfloor+\left\lfloor \frac{n+2}{6}\right\rfloor+\left\lfloor \frac{n+4}{6}\right\rfloor = \left\lfloor \frac{n}{2}\right\rfloor+\left\lfloor \frac{n+3}{6}\right\rfloor .
⌊
3
n
⌋
+
⌊
6
n
+
2
⌋
+
⌊
6
n
+
4
⌋
=
⌊
2
n
⌋
+
⌊
6
n
+
3
⌋
.
floor function
invariant