OFFSET
1,1
COMMENTS
The pairs are ordered by the smaller number. - David Wasserman, Jun 18 2002
LINKS
Amiram Eldar, Table of n, a(n) for n = 1..10000 (terms 1..1000 from T. D. Noe)
Eric Weisstein's World of Mathematics, Amicable Pair.
EXAMPLE
a(1) = gcd(220, 284) = 4;
a(2) = gcd(1184, 1210) = 2.
MATHEMATICA
With[{s = PositionIndex@ Array[DivisorSigma[1, #] &, 10^6]}, Flatten@ Map[GCD @@ # &, Apply[Join, Map[Function[n, Select[Subsets[Lookup[s, n], {2}], Total@ # == n &]], Sort@ Select[Keys@ s, Length@ Lookup[s, #] > 1 &]]]]] (* Michael De Vlieger, Oct 22 2017 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Jason Earls, Jun 11 2001
EXTENSIONS
More terms from David Wasserman, Jun 18 2002
a(22) corrected by T. D. Noe, Aug 15 2010
STATUS
approved