A241625 - OEIS

%I #11 May 10 2014 10:00:49

%S 1,3,4,7,6,6187272,8,15,13,196602,8105688,28,14

%N Smallest number m such that the GCD of the x's that satisfy sigma(x)=m is n.

%C This sequence is a sequel to A240667.

%C First unknown terms occur for n=14 and n=15.

%C Other large known terms occur at these indices: a(16)=2031554, a(25)=1355816, a(31)=8880128, a(80)=11532, a(97)=5488.

%C Small terms occur and are easily found when n belongs to A211656.

%C a(14) > 10^9. - _Michel Marcus_, May 09 2014

%e a(2) = 3, because the only x such that sigma(x)=3 is 2.

%e a(6) = 6187272, because the x's that satisfy sigma(x)=6187272 are [2651676, 2855646] and their GCD is 6.

%o (PARI) lista() = {lim = 12000000; nn = 100; out = "a241625.txt"; v = vector(lim, i, sigma(i)); w = vector(lim); for (i=1, lim, vi = v[i]; if (vi <= lim, if (w[vi] == 0, w[vi] = i, w[vi] = concat(w[vi], i)););); for (i=1, nn, got = 0; write1(out, i, " "); for (j=1, #w, wj = w[j]; if (gcd(wj) == i, got = 1; write(out, j);break;);); if (! got, write(out, );););}

%Y Cf. A000203, A211656, A240667.

%K nonn,more,nice

%O 1,2

%A _Michel Marcus_, Apr 26 2014