I will add Steve Finch's references to this entry in the OEIS: %I A018805 %S A018805 1,3,7,11,19,23,35,43,55,63,83,91,115,127,143,159,191,203,239,255,279, %T A018805 299,343,359,399,423,459,483,539,555,615,647,687,719,767,791,863,899,947, %U A018805 979,1059,1083,1167,1207,1255,1299,1391,1423,1507,1547,1611,1659,1763 %N A018805 Number of elements in the set {(x,y): 1<=x,y<=n, 1=gcd(x,y)}. ... where there is already the comment %F A018805 a(n) ~ (1/Zeta(2)) * n^2 = (6/pi^2) * n^2 as n goes to infinity (zeta is the Riemann zeta function and the constant 6/pi^2 is 0.607927...). - Ahmed Fares (ahmedfares(AT)my-deja.com), Jul 18 2001 As for triples, there is this: %I A071778 %S A071778 1,7,25,55,115,181,307,439,637,841,1171,1447,1915,2329,2881,3433,4249, %T A071778 4879,5905,6745,7861,8911,10429,11557,13297,14773,16663,18355,20791, %U A071778 22495,25285,27541,30361,32905,36289,38845,42841,46027,49987,53395 %N A071778 Number of ordered triples (a, b, c) with gcd(a, b, c) = 1 and 1 <= {a, b, c} <= n. ... for ordered triples. But I'm not sure if the numbers of unordered triples is there. Neil Sloane