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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 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,1

LINKS

Robert Israel, Table of n, a(n) for n = 1..1849

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

CROSSREFS

Cf. A000203, A240667, A241625, A241646, A241647, A241648, A241649, A241650.

Sequence in context: A130614 A114877 A152859 * A157547 A160879 A157562

Adjacent sequences:  A241644 A241645 A241646 * A241648 A241649 A241650

KEYWORD

nonn

AUTHOR

Michel Marcus, Apr 26 2014

STATUS

approved

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Last modified November 29 07:48 EST 2021. Contains 349416 sequences. (Running on oeis4.)