Assume {a,b,c} is a triple satisfying the required conditions. For every positive integer r, let Sr=ar+br+cr. We denote S=S1.
First, let us show that S divides S11k+1 for every non-negative integer k. We proceed by induction on k. For k=0,1,2, the claim is true by our assumptions on {a,b,c}. Let k≥2 and assume the result holds for k−2,k−1 and k; we will see it is true for k+1. We have that
S11k+1⋅S11=(a11k+1+b11k+1+c11k+1)(a11+b11+c11)=a11(k+1)+1+b11(k+1)+1+c11(k+1)+1+(ab)11(a11(k−1)+1+b11(k−1)+1)+(ac)11(a11(k−1)+1+c11(k−1)+1)+(bc)11(b11(k−1)+1+c11(k−1)+1)=S11(k+1)+1+((ab)11+(ac)11+(bc)11)S11(k−1)+1−(abc)11(a11(k−2)+1+b11(k−2)+1+c11(k−2)+1)=S11(k+1)+1+((ab)11+(ac)11+(bc)11)S11(k−1)+1−(abc)11S11(k−2)+1.
By the induction assumption, S divides S11k+1, S11(k−1)+1 and S11(k−2)+1; therefore, the above equality implies that S divides S11(k+1)+1, as we wanted to prove.
Consider the factorization x3+y3+z3−3xyz=(x+y+z)(x2+y2+z2−xy−xz−yz). If x,y,z are integers, it implies that every divisor of x+y+z also divides x3+y3+z3−3xyz. By taking x=a11004, y=b11004 and z=c11004, and recalling that S divides S11004, we deduce that S divides S33012−3(abc)11004. Since 33012≡1(mod11), we know that S divides S33012; therefore, S divides 3(abc)11004.
Assume p>3 is a prime factor of S. Since p divides 3(abc)11004, then, it divides a,b or c. With no loss of generality, assume p divides a; then, p divides b+c, as it divides S=a+b+c. But we also have that p divides a12+b12+c12, and looking modulo p, we get that a12+b12+c12≡012+b12+(−b)12≡2b12(modp). It follows that p divides b and, as a consequence, it divides c, contradicting the fact that a,b and c are coprime. We conclude that S does not have a prime divisor greater than 3.
Hence, S=2x3y for non-negative integers x and y. Finally, we will show that x,y≤1. If x≥2, we have that a12+b12+c12≡0(mod4). As the quadratic residues modulo 4 are 0 and 1, the only possibility is that a≡b≡c≡0(mod2), contradicting the coprimality of a,b,c. Similarly, if y≥2, we have that a12+b12+c12≡0(mod9) but, taking into account that for an integer m, the possible residues of m6 modulo 9 are 0 and 1, this implies that a≡b≡c≡0(mod3), which is again a contradiction.
Therefore, the possible values of S=a+b+c are 3 and 6, since a,b,c are positive integers and, consequently, the possible triples {a,b,c} are {1,1,1}, {1,2,3}, {1,1,4} and {2,2,2}. It is clear that the first one satisfies the conditions and that the last one is not a solution because a,b,c are not coprime. Now, {1,2,3} is not a solution either, since 1+2+3=6 does not divide 112+212+312 (this number has residue 2 modulo 3). To check that {1,1,4} satisfies the conditions, it suffices to note that 1r+1r+4r≡0(mod2) and 1r+1r+4r≡0(mod3) for every positive integer r.
We conclude that the solutions are {1,1,1} and {1,1,4}.