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A241647
Numbers m such that the GCD of the x's that satisfy sigma(x)=m is 2.
5
3, 126, 186, 399, 924, 1350, 1386, 1530, 1806, 2106, 2646, 2652, 2814, 2916, 3066, 3150, 3654, 3870, 4662, 4914, 6162, 6426, 6846, 6882, 6930, 7098, 7566, 7620, 8190, 8910, 9270, 10842, 11076, 12222, 12870, 14586, 14910, 15210, 15246, 15930, 16506, 17010
OFFSET
1,1
LINKS
EXAMPLE
We have sigma(68)=sigma(82)=126, and gcd(68, 82) = 2, hence 126 is in the sequence.
On the other hand, for x in [20, 26, 41], sigma(x)=42, and gcd(20, 26, 41)=1, hence 42 is not here, although gcd(20, 26) is 2.
MAPLE
N:= 10^5: # 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]=2, [$1..N]); # Robert Israel, Aug 18 2019
KEYWORD
nonn
AUTHOR
Michel Marcus, Apr 26 2014
STATUS
approved