Проверено
asg@asg-inet:~$ g++ a.c -lgmpxx -lgmp
asg@asg-inet:~$ ./a.out
X = -80538738812075974
Y = 80435758145817515
Z = 12602123297335631
X^3 = -522413599036979150280966144853653247149764362110424
Y^3 = 520412211582497361738652718463552780369306583065875
Z^3 = 2001387454481788542313426390100466780457779044591
X^3 + Y^3 + Z^3 = 42