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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
OFFSET
1,2
LINKS
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
KEYWORD
nonn
AUTHOR
Michel Marcus, Apr 26 2014
STATUS
approved