OFFSET
1,1
COMMENTS
First differs from A125639 at n = 12.
This sequence is infinite: if m is divisible by 6 and coprime to 5, then 5*m is a term.
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000
MATHEMATICA
ab[n_] := DivisorSigma[1, n] - 2*n; q[n_] := Module[{k = ab[n]}, k > 0 && ab[k] > 0]; Select[Range[360], q]
PROG
(PARI) ab(n) = sigma(n) - 2*n;
is(n) = {my(k = ab(n)); k > 0 && ab(k) > 0; }
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
Amiram Eldar, Apr 12 2024
STATUS
approved