use entity pointers.

ENTITY* num_1;
ENTITY* num_2;
ENTITY* num_3;
ENTITY* num_4;

then assign them inside their actions...

action entity_1()
{
num_1 = me;
}

or if you don't want actions, create them using pointers...

num_1 = ent_create("model.mdl",vector(0,0,0),NULL);