

A241646


Numbers m such that the GCD of the x's that satisfy sigma(x)=m is 1.


5



1, 12, 18, 24, 31, 32, 42, 48, 54, 56, 60, 72, 80, 84, 90, 96, 98, 104, 108, 114, 120, 128, 132, 140, 144, 152, 156, 168, 180, 182, 192, 216, 224, 228, 234, 240, 248, 252, 264, 270, 272, 280, 288, 294, 308, 312, 324, 336, 342, 360, 372, 384, 390, 408, 420
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OFFSET

1,2


LINKS

Robert Israel, Table of n, a(n) for n = 1..10000


EXAMPLE

We have sigma(6)=sigma(11)=12, and gcd(6, 11) = 1, hence 12 is in the sequence.
For x in [20, 26, 41], sigma(x)=42, and gcd(20, 26, 41)=1, hence 42 is here.


MAPLE

N:= 10^4: # for terms <= N
V:= Vector(N):
for x from 1 to N do
s:= numtheory:sigma(x);
if s <= N then
if V[s] = 0 then V[s]:= x
else V[s]:= igcd(V[s], x)
fi
fi
od: select(t > V[t]=1, [$1..N]); # Robert Israel, Aug 18 2019


CROSSREFS

Cf. A000203, A240667, A241625, A241646, A241647, A241648, A241649, A241650.
Sequence in context: A091013 A159886 A258914 * A181941 A206449 A241852
Adjacent sequences: A241643 A241644 A241645 * A241647 A241648 A241649


KEYWORD

nonn


AUTHOR

Michel Marcus, Apr 26 2014


STATUS

approved



