OFFSET
1,2
COMMENTS
This sequence is a sequel to A240667.
First unknown terms occur for n=14 and n=15.
Other large known terms occur at these indices: a(16)=2031554, a(25)=1355816, a(31)=8880128, a(80)=11532, a(97)=5488.
Small terms occur and are easily found when n belongs to A211656.
a(14) > 10^9. - Michel Marcus, May 09 2014
EXAMPLE
a(2) = 3, because the only x such that sigma(x)=3 is 2.
a(6) = 6187272, because the x's that satisfy sigma(x)=6187272 are [2651676, 2855646] and their GCD is 6.
PROG
(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, ); ); ); }
CROSSREFS
KEYWORD
nonn,more,nice
AUTHOR
Michel Marcus, Apr 26 2014
STATUS
approved