cp's OEIS Frontend

A241479 GCD of the solutions x of sigma(x) = sigma(n), where sigma(n) = A000203(n) = sum of divisors of n.

%I A241479 #15 Dec 19 2024 06:15:46
%S A241479 1,2,3,4,5,1,7,8,9,1,1,12,13,1,1,1,1,18,19,1,1,22,1,1,1,1,27,1,29,1,1,
%T A241479 32,1,1,1,36,37,1,1,1,1,1,43,1,45,1,1,3,49,50,1,1,1,1,1,1,1,1,1,1,61,
%U A241479 1,1,64,1,1,67,2,1,1,1,72,73,1,3,1,1,1,1,2
%N A241479 GCD of the solutions x of sigma(x) = sigma(n), where sigma(n) = A000203(n) = sum of divisors of n.
%C A241479 A variant of A240667 without zeros.
%H A241479 Antti Karttunen, <a href="/A241479/b241479.txt">Table of n, a(n) for n = 1..20000</a>
%H A241479 Max Alekseyev, <a href="https://oeis.org/wiki/User:Max_Alekseyev/gpscripts">PARI/GP Scripts for Miscellaneous Math Problems</a> (invphi.gp).
%F A241479 a(n) = A240667(A000203(n)).
%e A241479 a(6) = 1 since sigma(6) = 12 and sigma(11) = 12 and gcd(6, 11) = 1.
%o A241479 (PARI) sigv(n) =  select(i->sigma(i) == n, vector(n, i, i));
%o A241479 a(n) = gcd(sigv(sigma(n)));
%o A241479 (PARI) a(n) = gcd(invsigma(sigma(n))); \\ _Amiram Eldar_, Dec 19 2024, using _Max Alekseyev_'s invphi.gp
%Y A241479 Cf. A000203, A240667.
%K A241479 nonn
%O A241479 1,2
%A A241479 _Michel Marcus_, Apr 23 2014