a(n) = number of triples (a,b,c) of natural numbers a,b,c <= n with gcd(a,b)=gcd(b,c)=gcd(c,a)=1.

Terms

a(0) =1a(1) =4a(2) =13a(3) =22a(4) =55a(5) =64a(6) =133a(7) =172a(8) =247a(9) =280a(10) =469a(11) =508a(12) =781a(13) =868a(14) =997a(15) =1144a(16) =1621a(17) =1714a(18) =2323a(19) =2488a(20) =2785a(21) =3010a(22) =3907a(23) =4078a(24) =4837a(25) =5176a(26) =5833a(27) =6178a(28) =7627a(29) =7798