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
KEYWORD
nonn
AUTHOR
Michel Marcus, Apr 26 2014
STATUS
approved