OFFSET
1,1
LINKS
Robert Israel, Table of n, a(n) for n = 1..698
EXAMPLE
sigma(104) = sigma(116) = 210, and gcd(104, 116) = 4, hence 210 is in the sequence.
Likewise 6510 is obtained with sigma of [2600, 2900, 3464, 3716], with gcd 4.
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]=4, [$1..N]); # Robert Israel, Aug 18 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Michel Marcus, Apr 26 2014
STATUS
approved