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2021 CMIMC
2.7
2.7
Part of
2021 CMIMC
Problems
(1)
2021 Alg/NT Div 2 P7
Source:
3/2/2021
For each positive integer
n
,
n,
n
,
let
σ
(
n
)
\sigma(n)
σ
(
n
)
denote the sum of the positive integer divisors of
n
.
n.
n
.
How many positive integers
n
≤
2021
n \leq 2021
n
≤
2021
satisfy
σ
(
3
n
)
≥
σ
(
n
)
+
σ
(
2
n
)
?
\sigma(3n) \geq \sigma(n)+\sigma(2n)?
σ
(
3
n
)
≥
σ
(
n
)
+
σ
(
2
n
)?
Proposed by Kyle Lee
algebra
number theory